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Text Book on Radio 















Acknowledgment is hereby made to The West- 
inghouse Electric & Manufacturing Company, Gen¬ 
eral Electric Company, Radio Corporation of 
America, American Radio and Research Corpora¬ 
tion, Clapp-Eastham Company, Wm. J. Murdock 
Company, A. H. Grebe & Company, Inc., Crosley 
Manufacturing Company, K. B. Warner —“ Q.S.T.” 
— U. S. Bureau of Standards. And all my friends in 
the industry who in any way assisted me in the 
preparation of this work. 











TEXT BOOK 
ON RADIO 

By 

James R. Cameron 

n 

Author of 

“Radio for Beginners,” “Radio Dictionary,” 
“Motors and Motor Generators,” “Electricity 
for Projectionists,” “Motion Picture Projec¬ 
tion,” “Pocket Reference Book for Projec¬ 
tionists,” Etc. 


1922 



The TECHNICAL BOOK COMPANY 

New York City 











TKk5'5o 

,.Gz-\ 


Copyright in the United States, 1922 
Copyright in Great Britain, 1922 
Copyright in Canada, 1922 
By James B. Cameron 


Entered at Stationers Hall, 
London, England 


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Nova’22 



RADIO 


To the oft asked question: “What is wireless and 
how is it possible for one to hear signs, speech or 
music from a source several miles away, without any 
apparent connection and certainly without any me¬ 
chanical connection?” We are at first inclined to 
use the little boy’s expression on seeing the giraffe at 
the circus for the first time—“There ain’t no such 
animal,” but today this answer would immediately ■ 
be ridiculed by the vast army of radio fans through¬ 
out the country who daily “listen-in” to the numer¬ 
ous musical selections and speeches broad-casted from 
the various broadcasting stations. 

If w r e stop for a moment and think back to our 
elementary teachings regarding the nature and trans¬ 
mission of sound and light, we find that much of 
the mystery of wireless becomes very much matter- 
of-fact. Sound is merely some material body in 
motion. 

The vibrating of a piano or violin string or of the 
prongs of a tuning fork gives off a musical sound 
which can be heard by the human ear within a reason¬ 
able distance. We easily hear the strains of a brass 
band playing some few blocks away while seated at 
home with the doors and windows closed, the dis¬ 
charge of a big gun or an explosion (which is merely 
violent motion of matter) can be heard many miles 
away. When matter is set in motion it sets up a 
series of waves and it is on these waves that sound 
travels to our ears, the loudness or intensity of the 
sounds received by the ear depends upon the energy 

5 


6 


TEXT BOOK ON RADIO 


of the initial disturbance, and the distance the dis¬ 
turbance is from the ear. 

The discharge of the big gun several miles away 
sets up a series of oscillations or waves in the ether, 
and these waves carry the sound of the explosion to 
us at the rate of 1090 feet per second. When these 
waves reach the drum of our ear they produce the 
sensation we call sound. Much the same thing hap¬ 
pens in radio. 

A series of waves are set in motion by the creating 
of a disturbance in the ether by the transmitting 
aerial. The greater the disturbance, the further the 
waves will travel. These waves are termed “electro¬ 
magnetic waves, ’ 7 and travel at the rate of 186,000 
miles per second. These waves produce no sound to 
our ear on account of their very high frequency. It 
is to bring down this high frequency that the radio 
receiving set is necessary and a phone receiver em¬ 
ployed to make the sounds audible. 

In a broad sense, we claim that wireless telephony is 
a series of communications carried on between the 
broadcasting station and the receiving station through 
the medium of the ether. No one as yet has been 
able to tell us just what the nature of ether is, though 
we do know some medium exists throughout space 
which has the property of transmitting both light and 
electro-magnetic waves. 

Perhaps it would be as well at this point for us to 
study the question of light waves, as both the light 
waves and electro-magnetic waves have much in com¬ 
mon. For most purposes it is sufficiently accurate 
to take the velocity of light as 186,000 miles a second, 
(this is also the speed at which our electro-magnetic 
waves travel). 





LIGHT 1 WAVES 7 


A usual hypothesis which was first completely 
formulated by the great Dutch physicist—Huygens 
(1629-1695)—regards light like sound as a form of 
wave motion. This hypothesis met at first with two 
very serious difficulties; in the first place, light, un¬ 
like sound, not only travels with practical readiness 
through the best vacuum which can be obtained with 
an air-pump, but it travels without any apparent 
difficulty through the great interstellar spaces, which 
are probably infinitely better vacua than can be ob¬ 
tained by artificial means. 

If, therefore, light is a wave motion, it must be a 
wave motion of some medium which fills all space 
and yet which does not hinder the motion of the 
stars and planets. Huygens assumed such a medium 
to exist and called it “ether.” 

The second difficulty of the wave theory of light, 
was that it seemed to fail to account for the fact 
of straight-line propagation. Electro-magnetic waves, 
sound waves, water waves, and all of the forms of 
waves with which we are familiar bend readily around 
corners while light apparently does not. It was this 
difficulty, chiefly, which led many of the famous 
philosophers, including Sir Isaac Newton, to reject 
the wave theory of light. Within the last hundred 
years, however, this difficulty has been completely re¬ 
moved, and in addition other properties of light have 
been discovered, for which the wave theory offers the 
only satisfactory explanation. 

If the wave theory is to be accepted, we must con¬ 
ceive with Huygens that all space is filled with the 
medium called the ether, in which both light and 
electro-magnetic waves can travel. This medium can¬ 
not be like any of the other forms of matter, for if 





8 


TEXT BOOK. ON BADIO 


any of these forms existed in interplanetary space, 
the planets and other heavenly bodies would certainly 
be retarded in their motion. As a matter of fact, we 
know that no such retardation has ever been observed. 
The medium which transmits light and electro-mag¬ 
netic waves must, therefore, have a density which is 
infinitely smaller even in comparison with that of 
our lightest gases. The existence of such a medium 
is now universally assumed by physicists. 

Light waves are disturbances set up in the ether, 
probably by the vibrations of the minute corpuscles 
or electrons, of which the atoms of ordinary matter 
are supposed to be built, while sound waves are, dis¬ 
turbances set up in the air by the vibration of bodies 
of ordinary dimensions. Electro-magnetic waves are 
the waves used in wireless transmission, the waves 
being set in motion by the vibrations of the wires mak¬ 
ing up the aerial at the transmission station. These 
waves spread out in all directions with equal force, 
unless the direction of transmission be regulated by 
the use of directive aerials which would tend to make 
the wave transmission greater in any desired direc¬ 
tion. 

We have all stood on the banks of some river or 
lake, and as the result of having thrown a stone into 
the water, noticed the ripples on the surface of the 
water, how they spread out continually in the form 
of a circle, the ripples gradually becoming less dis¬ 
tinct the further they travel from the center. We 
can liken this to the transmission of wireless; the 
stone which disturbs the water corresponds to the 
transmission aerial which disturbs the air. The water 
of the lake to the ether, which we have already con¬ 
ceived fills all space, and the ripples on the surface 








SOUND WAVES 


9 


of the water to the electro-magnetic waves. Just as 
the ripples on the water gradually die out the further 
they travel from the source of the disturbance 
so do the magnetic waves become gradually weaker 
the further they travel from the transmission 
station. 

In the case of ripples on the surface of water it is 
plain to the eye that the waves are transmitted by 
the passing on of the up-and-down motion of the sur¬ 
face at the source. This is possible because at the 
surface of the water the particles of the water are 
held together by forces which resist their displace¬ 
ment. When one particle is displaced its neighbors 
are dragged with it to some extent. In technical terms 
the medium of transmission is said to have “elastic” 
properties and the forces brought into play are said 
to be elastic forces. The velocity of the waves de¬ 
pends on the nature and amount of these elastic 
forces. 

In the case of sound waves in air we do not ordina¬ 
rily see the vibrations of the particles of the air. The 
vibrations are quite small and the waves travel so 
fast that only under quite unusual conditions can they 
be made visible. But the mechanism by which the 
energy is transmitted is found to be of the same kind 
as in the case of water ripples. By the delicate elastic 
connections between neighboring portions of the air 
a vibration at one point is passed on to another. 
Sound waves are of another type than water waves 
only because the structure of air is different from 
that of water. Hence the elastic reaction to displace¬ 
ment is different in the two media. This is the sole 
cause of the differences between any two types of 


waves. 








10 


TEXT BOOK ON RADIO 


In the case of electromagnetic waves, often called 
“electric waves,” the displacements produced are of 
the kind considered in the section on capacity. The 
elastic reactions set up by such displacement cur¬ 
rents can be found by the same laws which determine 
the electric and magnetic forces due to any current. 
It is beyond the scope of this book to show the nature 
of these electrical elastic forces. It will be sufficient, 
however, to state that they are such as to produce 
waves in which (in free space) — 

(a) The displacement (and the electric field in¬ 
tensity) are at right angles to the direction of motion 
of the wave train. 

(b) The magnetic field intensity resulting from the 
displacement current is at right angles to the dis¬ 
placement and to the direction of the wave train. 

(c) The variations in the displacement (or the 
electric field intensity) and the magnetic field in¬ 
tensity are in phase. 

(d) The velocity of the waves is 300,000,000 meters 
per second, the same as the velocity of light (about 
186,000 miles per second). 

Such waves if started at a point in free space 
travel in all directions with the same velocity. They 
may be modified in various ways as they proceed. 
Thus, if they pass into a region of different dielectric 
constant, they are in general changed slightly in di¬ 
rection and partly reflected. Their energy is also 
absorbed to a greater or less extent in their passage 
through any medium. This absorption is greater for 
short than for long waves. In a perfect conductor 
no waves could be transmitted, since in such a medium 
there is no elastic opposition to the displacement of 
electricity. A perfectly conducting sheet would re- 






ELECTRO-MAGNETIC WAVES 


11 


fleet all of the wave energy falling on it. However, 
a conductor parallel to the direction of motion of a 
wave acts as a guide to the wave, through the action 
of currents induced in it by the varying magnetic 
field of the wave. It takes less energy from the 
waves, the better conductor it is. In the use of electric 
waves in radio communication all of these modifica¬ 
tions occur and serve to explain many of the irregu¬ 
larities of received signals. We can think of the space 
through which radio signals are sent as being bounded 
below by a sheet of varying conductivity (the earth’s 
surface) and above—at a distance of from 30 to 50 
miles—by another conducting region. This upper 
region, where the air is much rarefied, is a fairly 
good conductor, owing to its ionization by radiations 
from the sun. The region in between these conduct¬ 
ing layers is usually a good dielectric. Thus, this 
region acts more or less as a speaking tube does for 
sound waves, though its action is much more compli¬ 
cated. The electromagnetic waves are set up near 
the earth’s surface. They are partly transmitted as 
guided wave trains along the earth’s surface, modi¬ 
fied by refractions and absorption at its irregulari¬ 
ties; another part, however, goes off as space waves, 
which by reflections at the upper and lower layers of 
the conducting boundaries may recombine with the 
guided wave in such a way as either to add or sub¬ 
tract their effects, depending on circumstances. In 
the daytime the upper conducting boundary will be 
less definitely marked than at night, on account of 
partial ionization of the air by the sun’s radiations. 
Hence, there will be less reflection of the space wave 
in the daytime, and consequently the guided wave 
will not be assisted materially by any reflected or re- 





12 


TEXT BOOK ON BADIO 


fracted part of the space wave. In the night, how¬ 
ever, when the upper boundary is more sharply de¬ 
fined, there is more reflection of the space wave, and 
in general signals received at night are stronger than 
in daytime. Night signals are, however, more vari¬ 
able in intensity, particularly for short waves. This 
is especially true during the time when the sunset 
line is passing between two communicating stations. 
This is in general what we should expect, as the 
upper boundary would be quite variable under such 
circumstances. Clouds and other meteorological con¬ 
ditions would cause great variations in the sharp¬ 
ness of this boundary surface, and this may explain 
the rapid fluctuations in the strength of received sig¬ 
nals often observed. 

From all these considerations it can be seen that 
the conditions under which received signals will be 
most uniform in intensity are: 

(a) Transmission using long waves. 

(b) Transmission by daylight. 

(c) Transmission over short distances. 

(d) Transmission over uniform conducting sur¬ 

face of sea water. 

It is only under these conditions that the perform¬ 
ance of different transmitting stations can be fairly 
compared. 

There are three principal sources encountered in 
practice which make it difficult to receive readable 
radio signals: (1) Interference from transmitting 
stations whose signals it is not desired to receive, (2) 
strays or static, and (3) the “fading” of the strength 
of the received signal. 





ELECTKO-MAGNETIC WAVES 13 


Interference from other transmitting stations can 
to a large extent be eliminated by selection of fre¬ 
quency (wave length), particularly by the use of 
transmitting apparatus which will radiate only a 
single wave length or a narrow band of wave lengths. 
Laws have been enacted which are designed to mini¬ 
mize interference from other stations. Interference 
from transmitting stations using even the same wave 
length as the station which it is desired to receive can 
also be reduced by directional reception and to some 
extent by directional transmission, which are dis¬ 
cussed later. 

Strays are electrical disturbances giving rise to 
irregular interfering noises heard in the telephone 
receivers. They are also called ‘‘static,” “atmos¬ 
pherics,” “X’s, ” and other names. Investigations 
have shown that there are many different causes for 
these stray waves, but have by no means completely 
explained their sources. In any particular case the 
possibility of getting a readable signal depends on 
the ratio of the strength of the signal to the strength 
of the static at that time. Experienced operators have 
stated that it is possible to copy messages when the 
strays were four times as strong as the signals, but 
much difficulty is often experienced when the strays 
are much weaker than this. The most common type 
of strays produces a grinding noise in the telephones; 
this type causes the most serious trouble. Another 
type, which produces a hissing noise, is usually asso¬ 
ciated with snow or rain. Nearby lightning produces 
a sharp snap. Another type consists of crashes simi¬ 
lar to but stronger than the grinding noises first 
mentioned. By ‘ ‘ stray elimination ’’ is meant methods 





14 


TEXT BOOK ON RADIO 


for increasing the ratio of signal strength to stray 
strength. 

Strays are usually much more serious in the summer 
than in the winter, and more serious in tropical lati¬ 
tudes than in more temperate latitudes. Radio com¬ 
munication in the Tropics presents many special diffi¬ 
cult problems. 

Strays are the most serious limitation on radio 
communication. Transmitting stations of high power 
can be built, but if the strays are strong at a given 
time at the receiving station satisfactory communica¬ 
tion can not be maintained, at least not v r ith the 
ordinary types of receiving equipment. A great deal 
of careful investigation has been done to reduce the 
effects of strays. 

The use in particular ways of the three-electrode 
electron tube has resulted in considerably reducing 
the effects of strays as compared with the results ob¬ 
tained with earlier forms of receiving equipment. The 
use of sharply tuned receiving equipment and the 
use of a musical note in the transmitted signal will 
usually somewhat reduce the effect of strays. 

If the ordinary elevated type of antenna is used 
alone, a method for reducing strays which has given 
fairly satisfactory results has been the use of a re¬ 
ceiving circuit having a primary circuit containing 
considerable inductance and having the circuit 
containing the telephone receivers tuned to the 
audio frequency and loaded with considerable in¬ 
ductance. 

The most satisfactory results in stray elimination 
have been obtained by the use of various kinds of'di¬ 
rectional receiving antennas—that is, antennas which 
receive most strongly signals which are transmitted 





FADING 


15 


from a particular direction. Such antennas are dis¬ 
cussed later in this book and include not only par¬ 
ticular forms of the ordinary elevated antenna but 
also the coil antenna. The best results have been 
obtained by a combination of coil antennas and ground 
antennas. 

“Fading” or “swinging” is a rapid variation of 
the strength of signals received from a given trans¬ 
mitting station, the same circuit adjustments being 
used at the transmitting and receiving stations. Fad¬ 
ing is not usually observed at short distances from 
a transmitting station, but usually only at distances 
from the transmitting station which are at least some 
10 or 20 per cent of the normal transmitting range 
of the station. Fading is observed particularly on 
short wave lengths, especially under 400 meters, and 
is therefore most important in amateur communica¬ 
tion and in communication with airplanes and other 
special military applications. A certain transmitting 
station will be received with normal intensity for a 
few minutes; then for a minute or two the signals 
will become much louder; and then rapidly become 
much fainter and may become so weak as to be un¬ 
readable for a short time. Fading is usually observed 
particularly at night and usually only in transmis¬ 
sion over land. Fading variations may be very rapid, 
with a period of about one second, or very slow, with 
a period of one hour or more. Transmitting stations 
located on the seacoast seem to fade more than inland 
stations. The principal method of avoiding trans¬ 
mission difficulties caused by bad fading is to increase 
considerably the wave length of the transmitting sta¬ 
tion, when this is possible. Fluctuations of the re¬ 
ceived signal resembling fading may sometimes be 










16 


TEXT BOOK ON RADIO 


due to variations in the wave length or intensity of 
the transmitted wave, caused, for instance, by the 
position of the transmitting antenna being changed 
by wind. If the fluctuations are due to wave length 
variations and are not too rapid, it is possible to 
vary the tuning adjustments of the receiving set to 
follow the wave length variations. 

Theory of Production and Reception of Electro¬ 
magnetic Waves 

To produce a train of waves of any kind a vibrating 
body is necessary. The vibrations of this body have 
next to be communicated to a continuous medium, 
after which the elastic properties of the medium take 
care of the transmission of the waves. In the case 
of electromagnetic waves the vibrating body is an 
oscillating electric charge in a circuit (the sending 
antenna circuit), while the means by which these 
oscillations are communicated to free space can best 
be described in terms of the motion, of the lines of 
force which, when at rest, are used to picture the 
field about electric charges. 

These lines are to be looked upon as lines along 
which there is a displacement of electricity against 
the elastic force of the medium. Thus they can not 
exist in conductors (in which no such elastic forces 
exist). Under the action of the elastic forces the 
displaced electricity is continually urged to return 
to its position of rest. In other words, there is a 
tension along the lines of force. In addition there 
must be a pressure at right angles to the lines of 
force, otherwise those lines would always be straight 
and parallel under the action of the tensions. These 





PRODUCTION OP ELECTRO-MAGNETIC WAVES 17 


pressures can be thought of as arising from the repul¬ 
sion between the displaced charges of the same sign 
in neighboring lines. 

Every alternating current has associated with it a 
magnetic field which can be considered to be the sum 
of two components having entirely different charac¬ 
teristics called, respectively, the “induction field” and 
the “radiation field.” 

The induction field is the only one of importance 
in the operation of the apparatus ordinarily used 
with alternating currents of commercial frequencies, 
such as 60 cycles. The alternating currents by which 
the ordinary transformer operates are due to the 
induction field. The cross talk often noticed between 
adjacent telephone lines is caused by the induction 
field. The action of the induction field on near-by 
circuits is often spoken of as “transformer action.” 
If two coils are placed near together, interruptions 
in an alternating current passing through one coil 
will be reproduced in the other by the action of the 
induction field. The intensity of the induction field, 
due to a current in such a closed coil, decreases 
rapidly with the distance from the coil and is inversely 
proportional to the cube of the distance from the 
coil. Signals can be transmitted by the induction 
field, using alternating currents having frequencies 
from about 300 to 3000 cycles; this is called “induc¬ 
tion signaling. ’ ’ One of the applications of induction 
signaling has been to transmit signals from a sub¬ 
merged cable to a ship almost directly over the cable 
to aid the ship in finding its course. The induction 
field due to the ordinary type of elevated antenna 
is inversely proportional to the square of the distance 
from the antenna. The induction field is not im- 

2—Oct. 22. 





18 


TEXT BOOK ON RADIO 


portant in the usual applications of radio communica¬ 
tion. 

The radiation field is transmitted by wave motion. 
The intensity of the radiation field falls off with the 
distance from a transmitting station, but is inversely 
proportional to the distance, instead of being inversely 
proportional to the square or the cube of the dis¬ 
tance. The induction field due to a current in a coil 
at a distance of 10 miles from the coil is only one 
one-thousandth of the strength of the induction field 
at a distance of 1 mile from the coil. The radiation 
field due to a current in a coil at a distance of 10 
miles from the coil is one-tenth of the strength of 
the radiation field at a distance of 1 mile from the 
coil. For communication over any considerable dis¬ 
tance, it is therefore necessary to make use of the 
radiation field. 

For the ordinary type of elevated antenna, the in¬ 
tensity of the radiation field is greater than that of 
the induction field at distances from the transmitting 
station exceeding the wave length divided by 6.28. 

The strength of the radiation field at a given point 
due to an alternating current in the ordinary type 
of elevated transmitting antenna is directly propor¬ 
tional to the frequency. When the coil antenna is 
used for transmitting, the strength of the radiated 
field is proportional to the square of the frequency. 
It is therefore necessary to use high frequencies to 
get a radiation field sufficiently strong to allow suc¬ 
cessful communication. With the ordinary type of 
elevated antenna, the radiation field at a given point 
due to an alternating current having a frequency of 
1,500,000 cycles (wave length=200 meters) would be 
25,000 times as strong as the radiation field due to an 




RECEPTION OF ELECTRO-MAGNETIC WAVES 19 


alternating current having a frequency of 60 
cycles. 

The above statements are for radiation in free space. 
In actual communication part of the energy of the 
radiated field is, however, absorbed in the surface of 
the earth or in the surface of the ocean as the wave 
travels. This absorption effect is greater for high 
frequencies. It need not ordinarily be taken into 
account in short-distance work, but at distances 
greater than about 100 kilometers it becomes impor¬ 
tant. For this reason it is not possible to indefinitely 
increase the strength of the radiated field at a given 
distance by increasing the frequency. 

The statement is sometimes made that a circuit 
carrying an alternating current of low frequency, 
such as 60 cycles, does not radiate. This is not really 
true; radiation does occur, but is of very feeble in¬ 
tensity. 

Another statement sometimes made is that an 
“open” circuit can radiate, while a “closed” circuit 
can not; this is not true. All circuits are closed. 

As it has been shown that the electro-magnetic waves 
travel in every direction from its source, it is possible 
that any receiving station within range of the trans¬ 
mitting station will be capable of receiving the mes¬ 
sages sent out, providing they are tuned up to the 
same wave lengths. The length of the electro-mag¬ 
netic waves can be altered at will by altering the 
oscillatory circuit, but at present the waves vary in 
length from 150 to 20,000 meters. Most of the local 
broadcasting stations are sending out the concerts on 
a short wave length of 360 meters, while amateurs 
are restricted by the government to a 200 meter wave 
length for transmission. 





20 


TEXT BOOK ON EADIO 


That part of the wireless set that creates the elec¬ 
tro-magnetic waves at the transmission station is called 
the transmitter. To be able to fully understand the 
working principles of the transmitter and its connec¬ 
tions, it will be necessary to have at least an elemen¬ 
tary knowledge of electricity. 




ELECTRICITY 


No one knows exactly what electricity is, we do not 
even know what it consists of, we do know that elec¬ 
tricity and magnetism are one and the same. Elec¬ 
tricity is not matter nor yet is it energy, although it 
is a means of transmitting energy, and we know how 
to handle this force for this purpose. 

It is an undeniable fact that energy cannot be 
created nor can it be destroyed, but we can convert 
one kind of energy into energy of another kind. For 
example, should we light a fire under a vessel con¬ 
taining water we will convert the heat energy from 
the coals to steam energy in the vessel containing the 
water, and we could again change this steam energy 
into mechanical energy, as is done with the locomo¬ 
tive. 

It is also possible to convert mechanical energy into 
electrical energy, so by connecting the mechanical 
energy created by the steam to a dynamo we would 
produce electrical energy. 

It is also possible to convert electrical energy into 
mechanical energy. A motor is used for this purpose. 

The word dynamo is used to designate a machine 
which produces direct current as distinguished from 
the alternator or generator which produces alternat¬ 
ing current. A dynamo does not create electricity 
but produces an induced electric-motive force which 
causes a current of electricity to flow through a circuit 
of conductors in much the same manner as a pump 
causes water to flow through a pipe. The point to 
be settled in the minds of those taking up electricity 

21 


22 


TEXT BOOK ON BADIO 


is that the dynamo merely sets into motion some¬ 
thing already existing, by generating sufficient pres¬ 
sure to overcome the resistance to its movement. 

Although we speak of alternating and direct cur¬ 
rent, it should be clearly understood that it is impossi¬ 
ble to get a continuous current with a dynamo. The 
current is really a pulsating one, but the pulsations 
are so small and follow each other so quickly that 
the current is practically continuous. 

Electromotive Force. When a difference of elec¬ 
trical potential exists between two points, there is 
said to exist an electromotive force, or tendency to 
cause a current to flow from one point to the other. 
This electromotive force is analogous to the pressure, 
caused by a difference in level of two bodies of water 
connected by a pipe. The pressure tends to force 
the water through the pipe, and the electromotive 
forces tends to cause an electric current to flow. 

Electromotive force is commonly designated by the 
letters E. M. F. or simply E. It is also referred to 
as pressure or voltage. 

Current. A current of electricity flows when two 
points, at a difference of potential, are connected by a 
wire, or when the circuit is otherwise completed. Simi¬ 
larly, water flows from a high level to a lower one, 
when a path is provided. In either case the flow 
can take place only when the path exists. Hence 
to produce a current it is necessary to have an elec¬ 
tromotive force and a closed circuit. The current 
continues to flow only as long as the electromotive 
force and closed circuit exists. 

The strength of a current in a conductor is defined 
as the quantity of electricity which passes any point 





ELECTRICITY 23 


in the circuit in a unit of time. Current is designated 
by the letter C or I. 

Resistance . Resistance is that property of matter, 
in virtue of which bodies oppose or resist the free 
flow of electricity. Water passes with difficulty 
through a small pipe of great length or through a 
pipe filled with stones or sand, but very readily 
through a large, clear pipe of short length. Like¬ 
wise, a small wire of considerable length and made 
of poor conducting material offers great resistance 
to the passage of electricity, but a good conductor of 
short length and large cross-sections offers very little 
resistance. 

Resistance is designated by the letter R. 

Volt, Ampere and Ohm. The volt is the practical 
unit of electromotive force. 

The ampere is the practical unit of current. 

The ohm is the practical unit of electrical resistance. 
The microhm is one millionth of an ohm, and the 
megohm is one million ohms. 

The International ohm, as nearly as known, is the 
resistance of a uniform column of mercury 106.3 
centimeters in length by one square millimeter in 
cross-section at a temperature of zero centigrade. 

The ampere is the strength of current which, when 
passed through a solution of silver nitrate, under suit¬ 
able conditions, deposits silver at the rate of .001118 
gram per second. 

The volt is equal to the E. M. F. which, when 
applied to a conductor having a resistance of one 
ohm, will produce in it a current of one ampere. 

All substances resist the passage of electricity, but 
the resistance offered by some is very much greater 





24 


TEXT BOOK ON RADIO 


than that offered by others. Metals have by far the 
least resistance, and of these, silver possesses the least 
of any. In other words, silver is the best conductor. 
If the temperature remains the same, the resistance 
of a conductor is not affected by the current passing 
through it. A current of ten, twenty or any number 
of amperes may pass through a circuit, but its resist¬ 
ance will be unchanged with constant temperature. 
Resistance is affected by the temperature and also 
by the degree of hardness. Annealing decreases the 
resistance of a metal. 

Conductance is the inverse of resistance; that is, if 
a conductor has a resistance of R ohms, its conduct¬ 
ance is ^ 

equal to —. 

R 

Resistance Proportional to Length . The resistance 
of a conductor is directly proportional to its length. 
Hence, if the length of a conductor is doubled, the 
resistance is doubled, or if the length is divided, say 
into three equal parts, then the resistance of each 
part is one-third the total resistance. 

Resistance Inversely Proportional to Cross-Section. 
The resistance of a conductor is inversely proportional 
to its cross-sectional area. Hence the greater the 
cross-section of a wire the less is its resistance. There¬ 
fore, if two wires have the same length, but one has 
a cross-section three times that of the other, the re¬ 
sistance of the former is one-third that of the latter. 

As the area of a circle is proportional to the square 
of its diameter, it follows that the resistances of round 
conductors are inversely proportional to the squares 
of their diameters. 






ELECTKICITY 


25 


Specific Resistance. The specific resistance of a 
substance is the resistance of a portion of that sub¬ 
stance of unit length and unit cross-section at a stand¬ 
ard temperature. The units commonly used are the 
centimeter or the inch, and the temperature that of 
melting ice. The specific resistance may therefore 
be said to be the resistance (usually stated in mi* 
crohms) of a centimeter cube or of an inch cube at 
the temperature of melting ice. If the specific resist¬ 
ances of two substances are known, then their related 
resistance is given by the ratio of the specific resist¬ 
ance. 

Calculation of Resistance. It is evident that resist¬ 
ance varies directly as the length, inversely as the 
cross-sectional area, and depends upon the specific 
resistance of the material. 

If a circuit is made up of several different materials 
joined in series with each other, the resistance of 
the circuit is equal to the sum of the resistances of 
its several parts. In calculating the resistance of such 
a circuit, the resistance of each part should first be 
calculated, and the sum of these resistances will be 
the total resistance of the circuit. 

Resistance Affected by Heating. The resistance of 
metals depends upon the temperature, and the re¬ 
sistance is increased by heating. The heating of some 
substances, among which is carbon, causes a decrease 
in their resistance. The resistance of the filament of 
an incandescent lamp when lighted is only about half 
as great as when cold. All metals , however, have 
their resistance increased by a rise in temperature. 
The percentage increase in resistance with rise of 
temperature varies with the different metals, and 





26 TEXT BOOK ON RADIO 


varies slightly for the same metal at different tem¬ 
peratures. The increase is practically uniform for 
most metals throughout a considerable range of tem¬ 
perature. The resistance of copper increases about .4 
per cent, per degree Centigrade. The percentage in¬ 
crease in resistance for alloys is much less than for 
the simple metals. Standard resistance coils are 
therefore made of alloys, as it is desirable that their 
resistance should be as nearly constant as possible. 

Quantity, Energy and Power 

Quantity. The strength of a current is determined 
by the amount of electricity which passes any cross- 
section of the conductor in a second; that is, current 
strength expresses the rate at which electricity is con¬ 
ducted. The quantity of electricity conveyed evi¬ 
dently depends upon the current strength and the 
time the current continues. 

The Coulomb. The coulomb is the unit of quantity 
and is equal to the amount of electricity which passes 
any cross-section of the conductor in one second when 
the current strength is one ampere. If a current of 
one ampere flows for two seconds, the quantity of elec¬ 
tricity delivered is two coulombs, and if two amperes 
flow for one second the quantity is also two coulombs. 
With a current of four amperes flowing for three 
seconds, the quantity delivered is 12 coulombs. The 
quantity of electricity in coulombs is therefore equal 
to the current strength in amperes multiplied by the 
time in seconds. 

Energy. Whenever a current flows, a certain 
amount of energy is expended, and this may be trans¬ 
formed into heat, or mechanical work, or may produce 





ELECTRICITY 


27 


chemical changes. The unit of mechanical energy is 
the amount of work performed in raising a mass of 
one pound through a distance of one foot, and is 
called the foot-pound. The work done in raising any 
mass through any height is found by multiplying the 
number of pounds in that mass by the number of 
feet through which it is lifted. Electrical work may 
be determined in a corresponding manner by the 
amount of electricity transferred through a difference 
of potential. 

The Joule. The joule is the unit of electrical 
energy, and is the work performed in transferring 
one coulomb through a difference of potential of one 
volt. That is, the unit of electrical energy is equal 
to the work performed in transferring a unit of 
quantity of electricity through a unit of difference 
of potential. It is evident that if 2 coulombs pass 
in a circuit and the difference of potential is one volt, 
the energy expended is 2 joules. Likewise, if 1 
coulomb passes and the potential difference is 2 volts, 
then the energy expended is also 2 joules. Therefore, 
to find the number of joules expended in a circuit, 
multiply the quantity of electricity by the potential 
difference through which it is transferred. 

Power. Power is the rate of doing work, and ex¬ 
presses the amount of work done in a certain time. 
The horsepower is the unit of mechanical energy, and 
is equal to 33,000 foot-pounds per minute, or 550 foot¬ 
pounds per second. A certain amount of work may 
be done in one hour or two hours, and in stating the 
work done to be so many foot-pounds or so many 
joules, the rate at which the work is done is not ex¬ 
pressed. Power, on the other hand, includes the rate 
of working. 





28 TEXT BOOK ON RADIO 


It is evident that if it is known that a certain 
amount of work is done in a certain time, the rate 
at which the work is done, or the power, may be ob¬ 
tained by dividing the work by the time, giving the 
work done per unit of time. 

The Watt. The electrical unit of power is the watt, 
and is equal to one joule per second; that is, when 
one joule of w r ork is expended in one second, the 
power is one watt. If the number of joules expended 
in a certain time is known, then the power in watts 
is obtained by dividing the number of joules by the 
time in seconds. 

The power is obtained by multiplying the current 
by the voltage, or by multiplying the square of the 
current by the resistance. 

The watt is sometimes called the volt-ampere . 

For large units the kilowatt is used, and this is 
equal to 1,000 watts. The common abbreviation for 
kilowatt is K. W. The kilowatt-hour is a unit of 
energy, and is the energy expended in one hour when 
the power is one kilowatt. 

Equivalent of Electrical Energy in Mechanical 
Units. The common unit of mechanical energy is the 
foot-pound, and from experiment it has been found 
that one joule is equivalent to .7373 foot-pound; that 
is, the same amount of heat will be developed by one 
joule as by .7373 foot-pound of work. 

As one horse-power is equal to 550 foot-pounds per 
second, it follows that this rate of working is equiva¬ 
lent to 

550 

-= 746 joules per second (approx.). 


.7373 






ELECTRICITY 


29 


Hence one horse-power is equivalent to 746 watts. 
Therefore, to find the equivalent of mechanical power 
in electrical power, multiply the horse-power by 746; 
and to find the equivalent of electrical power in me¬ 
chanical power, divide the number of watts by 746. 

Ohms Laiv. Ohms law is merely the fundamental 
principle on which most of electrical mathematics are 
worked. 

A series of formulas used by electricians in figuring 
voltage, amperage and resistance: 

Formula 1 

To find the amount of current flowing in a circuit 
divide the voltage by the resistance, or 

Electric Motive Force 

Current =- 

Resistance 

For instance, if we have a line voltage of 100 and our 
circuit has resistance of 5 ohms, then by dividing 
100 by 5, we would get our amperage. 

5 ) 100 ( 20 
100 


so we would have 20 amperes. 

Formula 2 

To find the amount of resistance in a circuit, divide 
the voltage by the amount of amperage drawn, or 

Electric Motive Force 


Resistance = 


Current 








30 


TEXT BOOK ON RADIO 


For instance, suppose we have a line voltage of 100 
and are using 20 amperes, then by dividing the 
100 by 20 we would get the amount of resistance 
we have in our circuit. 

20 ) 100 ( 5 
100 


so we would have 5 ohms resistance in our circuit. 

Formula 3 

'* 

To find the voltage of a circuit, multiply the amount 
of amperes drawn by the amount of resistance, or 
Electric Motive Force = Amperes Times Resistance 

For example: If we were using 20 amperes and our 
circuit was offering 5 ohms resistance, then by 
multiplying 20 by 5 we would get our voltage. 

20 amperes 
5 ohms 

100 volts 

To find Volts. Multiply number of Amperes bj r 
amount of Resistance. 

To find Resistance. Divide Voltage by Amperage. 

To find Amperage. Divide Voltage by Resistance. 

To find Watts. Multiply Voltage by Amperage. 

To find Amps. Divide Watts by Volts. 

To find Volts. Divide Watts by Amperage. 








GENERATION OF ELECTRICITY 


Everyone is acquainted with the horseshoe magnet 
and the small pocket compass, and these two articles 
will serve as an illustration. 

Now if one of the legs of the horseshoe magnet be 
brought near the compass, it will be found that one 
end of the needle will be attracted to it, whilst if the 
other leg be presented the other end of the needle is 
attracted. One leg, at its end, has north polarity, 
because it attracts the south pole of the compass 
needle, whilst the other end, having south polarity, at¬ 
tracts the north end of the needle, so that between the 
ends of the two legs there exists what is known as a 
“magnetic field,” or space wherein magnetic lines of 
force are present. These lines of force are invisible, 
but if the magnet be laid on a table, and a piece of 
paper put over it, and if on the paper be sprinkled 
some iron filings it will be found, when the paper 
is tapped by the finger, that these filings group them¬ 
selves around the ends of the magnet in circles, being 
closer together at the ends than further away, or 
higher up towards the bend of the horseshoe. The 
magnetic field is the most dense between the legs of 
the magnet at their ends. If a copper wire be passed 
up and down between the ends of the legs an electric 
current will be induced in the wire, its direction of 
flow varying with the upward and downward motion 
of the wire. In this case the electricity is obtained 
from the magnet by “induction,” this being the ele¬ 
mentary principle upon which all dynamos, whether 

31 


32 


TEXT BOOK ON RADIO 


for lighting or power, is based. In the dynamo the 
horseshoe is replaced by electro-magnets, the large 
stationary pieces of soft iron surrounded with covered 
copper wire, whilst the armature, the part which 
revolves, replaces the thin pieces of copper wire in 
the' above simple experiment. The armature does not 
touch the magnets, and there is no friction except that 
in the bearings of the armature shaft, in which it is 



Fig. 1—Generator 


necessary to revolve, and which is made as easy as 
possible by a liberal supply of oil. It will also be 
seen that the electricity is not pumped from the at¬ 
mosphere, but is simply the revolution of a bundle of 
copper wires between the poles of a powerful electro¬ 
magnet. The ends of the electro-magnets are thickened 
out, and each one made semi-circular so that the arma¬ 
ture may revolve between the north and south poles 
and the electro-magnets, consisting of soft iron, are 
wound round with insulated copper wire, so that a 














GENERATION OF ELECTRICITY 


33 


portion of the electricity generated in the armature 
may be shunted around them and so keep always, 
whilst the dynamo is in action, as powerful electro¬ 
magnets. When the dynamo is stopped, these magnets 
retain a small amount of magnetism, which is grad¬ 
ually strengthened to its maximum as the armature is 
started revolving, the dynamo “building up” as it is 
termed. Anyone who has watched the starting up 
of a dynamo will have noticed that when running 
slowly the lamp connected to it as “pilot” gradually 



Fig. 2—Three Unit Set 


shows a red filament, which becomes brighter, as the 
revolutions increase, until, when the correct speed is 
reached for which the dynamo w r as designed, the right 
voltage will show on the voltmeter and the pilot lamp 
attain its full brilliancy. 

The armature of the dynamo is the only part which 
revolves, and this consists of a steel shaft supported 
in bearings at each end, to which the pulley is at¬ 
tached to receive the belt for transmitting the power 
from the engine to the dynamo. On the shaft are 
built up thin sheets of soft iron provided with grooves 
in which the different sections of insulated copper 


3 















34 TEXT BOOK ON EADIO 


wire are laid lengthwise, their ends being connected 
to what is called the “commutator” fastened to the 
shaft. This consists of bars of copper made into a 
drum, each bar being insulated from its neighbor by 
means of strips of mica, and on the commutator rest 
lightly the carbon or copper brushes to convey the 
electricity to the lamps or motors. 

The number of coils of wire on the armature de¬ 
pends upon the voltage the dynamo is designed to 



Generator 
Fig. 3 

give, and the speed at which it has to run, also upon 
the strength of the magnetic field of the electro-mag¬ 
nets; and the thickness of these conductors will de¬ 
pend upon whether it has to give a large or small 
current strength. If the voltage is to be high, and 
small current strength, many conductors of fine wire 
are employed; if the voltage required is to be low, 



















































ALTERNATORS 


35 


and large current strength, a few sections of thick 
wire are required. 

A machine as above described is known as a con¬ 
tinuous-current dynamo, to distinguish it from an 
‘ 4 alternator, ’ ’ and the current obtained from it flows 
in a continuous circuit from the positive brush or 
collector on the commutator, through the lamps or 
motors, and completes the circuit to the other brush. 

The mistaken notion of electricity being obtained 
by friction has probably arisen from the fact that, 
resting on the top and bottom of the commutator are 
carbon or copper brushes, but these are for the pur¬ 
pose of turning the currents, which are generated in 
• the armature as alternating currents, into one direc- 



Fig. 4—Four Bearing, Ring-oiled Set 


tion. They also act as collectors to convey the elec¬ 
tricity to the external circuit for lamps, motors, or 
other electricity-consuming devices, and do not offer 
practically any friction, only resting lightly against 
the surface of the revolving commutator. 

For supplying extensive areas such as towns where 














36 TEXT BOOK ON RADIO 


the demand for electricity is scattered, alternating- 
current machines or “alternators” are employed 
which do not require commutators, the high voltage 
generated, 2,000 volts and upwards, being led to trans¬ 
former stations, where it is reduced, by means of sta¬ 
tionary transformers, to 110 and 220 volts for feed¬ 
ing lamps direct, or for motors and other uses. The 
field magnets of these alternators are energized by a 
continuous or direct current supplied from a small 
dynamo generally fixed on the alternator shaft, and 
running at the same speed. 







rOio 








A 




rfr 


.m&l 


ZZ ' 1 '&S&'— | 1- 


«■> 


RSWiTi 


Usual 







$ 

«•* 


Fig. 5 








































ALTERNATING CURRENTS 


A continuous or direct current is one of uniform 
strength always flowing in one direction, while an 
alternating current is continually changing both its 
strength and direction. The various principles and 
facts concerning direct current distribution apply also 
to alternating current systems. But in addition to 
the simple phenomena due to the resistance, which 
occur with direct currents, there are certain addi¬ 
tional factors that must be considered in connection 
with alternating current transmission. 

The flow of a direct current is entirely determined 
by the ohmic resistance of the various parts of the 
circuit. The flow of an alternating current depends 
upon not only the resistance, but also upon any in¬ 
ductance (self or mutual) or capacity that may be 
contained in or connected with the circuit. These 
two factors, inductance and capacity, have no effect 
upon a direct current after a steady flow has been 
established, which usually requires only a fraction 
of a second. In an alternating current circuit either 
or both of them may be far more important than 
the resistance and in some cases may entirely control 
the action of the current. Alternating current prob¬ 
lems involving the consideration of three factors are 
usually more complicated and difficult to solve than 
those relating to direct currents. By an extension 
of the principles and methods employed for direct 
currents, however, alternating current systems can be 
designed correctly and without great difficulty. 

38 


* 


FREQUENCY 


39 


The only reason practically for employing alter¬ 
nating currents for electric lighting and power pur¬ 
poses is the economy effected in the cost of transmis¬ 
sion, which is accomplished by the use of high volt¬ 
ages and transformers. The cross section of a wire to 
convey a given amount of electrical energy in watts 
with a certain 11 drop ’ ’ or loss of potential in volts, is 
inversely proportional to the square of the voltage 
supplied; that is, it requires a wire of only one-quarter 
the cross-section and weight if the initial voltage is 
doubled. The great advantage thus obtained by the 
use of high voltages can be realized either by a 
saving in the weight of wire required or by trans¬ 
mitting the energy to a greater distance with the same 
weight of copper. 

When the alternating current, or emf., has 
passed from zero, to its maximum value, to zero, in 
one direction, then from zero, to its maximum value, 
to zero, in the other direction, the complete set of 
values passed through repeatedly during that time is 
called a cycle. This cycle of changes constitutes a 
complete ; period, and since it is repeated indefinitely 
at each revolution of the armature the currents pro¬ 
duced by such an emf. are called periodic cur¬ 
rents. The number of complete periods in one second 
is called the frequency of the pressure or current. 

The term frequency is applied to the number of 
cycles completed in a unit of time—one second. The 
word alternations is sometimes used to express the 
frequency of an alternator, meaning the number of 
alternations per minute. In practice the frequency 
is usually expressed in cycles. An alternation is half 
a period or cycle; since the current changes its direc¬ 
tion at each half cycle, it follows that the number of 






40 


TEXT BOOK ON RADIO 


alternations or reversals is twice the number of 
cycles. 

If the current from an alternator performed the 
cycle sixty times a second, it would be said to have a 
frequency of 60 cycles, which would mean 120 alter¬ 
nations per second, or 120 X 60 seconds = 7200 alter¬ 
nations per minute. 

The frequency of an alternating current is always 
that of the emf. producing it. 

Unless otherwise specified, frequencies are in the 
term of cycles, thus: a frequency of 60 means 60 
cycles. The frequency of commercial alternating cur¬ 
rent depends upon the work it is expected to do. 
For power a low frequency is desirable, frequencies 
for this purpose varying from 60 down to 25. 

For lighting work frequencies from 60 to 125 are 
in general use. Very low frequencies cannot be used 
for lighting owing to the flickering of the lamps. A 
number of central stations have adopted a frequency of 
60 as a standard for lighting and power transmission. 

For wireless w y ork the frequency must be very high, 
amateurs today are using a 1,500,000 cycle current 
for transmission. 

Most of the peculiarities that alternating current 
exhibits, as compared with direct current, are due 
more or less to the fact that an alternating current is 
constantly changing, whereas a continuous current 
flows uniformly in one direction. When a current 
flows through a wire it sets up a magnetic field around 
the wire, and since the current changes continually 
this magnetic field will also change. Whenever the 
magnetic field surrounding a wire is made to change, 
an emf. is set up in the wire, and this induced 
emf. opposes the current. For example, when the 






REACTANCE 


41 


current rises in the positive direction, the magnetism 
increases, in let us say, the clockwise direction about 
the conductor; after the current passes the maximum 
value and begins to decrease, the lines of force com¬ 
mence to collapse, reaching zero value when the cur¬ 
rent reaches zero; then when the current rises in the 
negative direction the magnetic lines expand in the 
counter-clockwise direction, and so on. The result is 
that the counter emf. of self-induction, instead 
of being momentary, as when the current is made 
and broken through a conductor, is continuous, but 
varies in value like the applied emf. and the cur¬ 
rent. The value of an induced emf. is propor¬ 
tional to the rapidity with which lines of force are 
cut by the conductor, and as the lines of force vary 
most rapidly when passing the zero point (changing 
from -j- to —) or vice versa , the induced emf. is 
maximum at the moment. 

When the current, and therefore the magnetism, is 
at the maximum value in either direction, its strength 
varies very little within a given momentary period 
of time, and consequently the induced emf. is zero 
at the moment the current and magnetism is at maxi¬ 
mum, the emf. of self-induction not rising and 
falling in unison with the applied emf. and the 
current, but lagging behind the current exactly a 
quarter of a cycle. 

This property of a wire or coil to act upon itself 
inductively (self-induction) or of one circuit to act 
inductively on another independent circuit (mutual 
induction) is termed Inductance . 

The Unit or Coefficient of inductance is called the 
henry, the symbol for which is L. 

Many devices met with an alternating current work 








42 


TEXT BOOK ON RADIO 


have this property of inductance. A long transmis¬ 
sion line has a certain amount of it, as have induction 
motors and transformers. 

The effect of inductance in an alternating current 
circuit is to oppose the flow of current on account of 
the counter emf. which is set up. This opposition 
may be considered as an apparent additional resist¬ 
ance and is called reactance to distinguish it from 
ohmic resistance. 

Reactance is expressed in ohms, like resistance, be¬ 
cause it constitutes an opposition to the flow of the 
current. Unlike the resistance, however, this opposi¬ 
tion does not entail any loss of energy because it is 
due to a counter pressure and is not a property 
analogous to friction. Its effect in practice is to 
make it necessary to apply a higher emf. to a 
circuit in order to pass a given current through it 
than would be required if only the resistance of the 
circuit opposed the current. 

Alternating currents are generated at various fre¬ 
quencies, covering a remarkably wide range. Depend¬ 
ing on their application, the frequencies in practical 
use fall into three well-defined classes: 

(a) Commercial frequencies, which nowadays gen¬ 
erally mean 25 or 60 cycles per second. 

(b) Audio frequencies, which are usually around 
500 to 1000 cycles per second but may extend as high 
as 10,000 cycles per second. 

(c) Radio frequencies, usually between 20,000 and 
2,000,000, but extending in extreme cases down to 
perhaps 10,000 and up to three hundred million cycles 
per second. 

Commercial frequencies are used for lighting and 
power. The great machines in the central stations 





AUDIO FREQUENCIES 


43 


which supply our cities with current operate at these 
frequencies. 

Audio frequencies are those conveniently heard in 
the telephone. When alternating currents are sent 
through a telephone, the diaphragm of the latter vi¬ 
brates. The vibrations are heard as sound. The more 
rapid the vibrations, the shriller the tone. Vibrations 
at the rate of 4,000 or 5,000 per second give a shrill 
whistle, while the lowest notes of a bass voice have 
somewhat under 100. If a 500-cycle generator sup¬ 
plies current to a spark gap and the spark jumps 
once on the positive and once on the negative half¬ 
wave, then at the receiving station the signal is heard 
in the telephone as a musical tone of 1000 vibrations 
per second. 

Radio frequencies occur in the circuits of radio ap¬ 
paratus, for instance, in an antenna. They are too 
rapid to cause a sound in a telephone which can be 
heard by the human ear. They may be generated 
by dynamo-electric machines of highly specialized con¬ 
struction, but are usually produced by other means. 

To show how the methods described in the preceding 
sections are applied in actual generators, a few typical 
machines used in radio sets will be briefly described. 
Whether or not these are of the latest design is not 
important. Changes of detail are constantly being 
made, but they do not affect the principles used and 
can be readily understood after the workings of simi¬ 
lar machines have been grasped. The examples of 
machines here given will also illustrate how the form 
of generator and the auxiliaries used with it are in¬ 
fluenced by the source of power available for driv¬ 
ing it. 

The generator is only one part of a unit for con- 








44 


TEXT BOOK ON RADIO 


verting energy into the electrical form. The other 
part depends on the source of energy available; it may 
be heat derived from coal or gasoline; it may be fall¬ 
ing water, moving air, human muscles, or a charged 
storage battery. 

Crank Driven .—The field radio pack set furnishes 
an example of a self-contained generating unit driven 
by hand. These sets have been changed somewhat 
from time to time and can therefore be described 
only in a general way. The generator is cylindrical in 
shape and is entirely incased, including the ends, in 
a metal shell. At one end of it is a flywheel for 
equalizing the speed. At the other is the train of 
gears, running in oil and inclosed in a housing, 
through which power is transmitted from the crank 
shaft to the generator shaft. The crank shaft is 
turned by means of a pair of cranks. 

The alternator is a 250-watt, 500-cycle machine of 
the revolving armature type. The exciter is built in 
with the alternator, so that the two have but one 
frame and one set of bearings, and the same shaft 
carries both armatures. Near one end, on opposite 
sides of the shell, is a pair of holes giving access to 
the d.c. brushes which bear on the commutator of the 
exciter and near the other end are similar holes for 
the a.c. brushes that bear on the collector rings. The 
crank is turned at the rate of 33 to 50 r.p.m., depend¬ 
ing on the machine (that is, the date of the model), 
and the generators make 3300 to 5000 r.p.m., the 
cranks being geared to them at a ratio of 1 to 100. 






ELECTRICAL RESISTANCE 


Electrical resistance is that property of anything in 
an electric circuit which will resist the flow of cur¬ 
rent. The effect of resistance is to produce heat. 

The unit of electrical resistance is the ohm, and is so 
named after Dr. G. S. Ohm who gave us the series of 
formulas now known as Ohm’s Law; it will be neces¬ 
sary to thoroughly understand the working of this law 
to be able to work out any of the numerous problems 
in electrical resistance. Ohm’s Law states that: The 
current is directly proportional to the voltage and 
inversely proportional to the resistance. This means 
that if the voltage of a circuit be increased the cur¬ 
rent will proportionally increase, and should the re¬ 
sistance of a circuit be increased then the current will 
be proportionately decreased. Should the voltage be 
decreased there will be a proportional decrease in the 
current, if the resistance in the circuit is decreased 
there will be a proportional increase in current. Ex¬ 
pressed mathematically 

Electric Motive Force 

Current —- 

Resistance 

Current is equal to the Electric Motive Force (Volt¬ 
age) divided by the Resistance (in ohms) or 

E 

R 

If by dividing the voltage by the resistance we get 
the amount of current, then by dividing the voltage 

45 



46 TEXT BOOK ON RADIO 


by the current we will naturally get the amount of 
resistance in our circuit, or— 

EMF 

R =- 

C 

and so to find the voltage all we have to do is to 



multiply the current by the amount of resistance in 
our circuit, or— 

E M F = C X R 

It will thus be seen that providing we have two known 
quantities the third unknown quantity can easily be 
obtained by the use of one of the above formulas; for 
instance, let us suppose that we have a line voltage 


























RESISTANCE 


47 


of 100 and our circuit has a total resistance of 5 ohms, 
then by dividing the 100 (volts) by 5 (ohms) we find 
our current to be 20 (amperes). 

Providing we knew there was a line voltage of 100 
and we were drawing 20 amps, then by dividing the 
100 (volts) by 20 (amperes) we would get the amount 
of resistance in our circuit, which would be 5 (ohms). 

By the foregoing it is evident that the amount of 
current we will get depends on the emf. and the 
amount of resistance in our circuit. 

Resistance is the inverse to conductivity. 

Current encounters resistance when passed over 
any conductor. Copper, silver and aluminum are 
good conductors, so offer very little resistance, while 



Fig. 7—Vernier Rheostat 


metals like iron and German silver are poor con¬ 
ductors and offer a much higher resistance to the flow 
of current. 

The resistance of any conductor increases, as the 
length of the conductor is increased, as the diameter 
of the conductor is decreased; or as the temperature 
of conductor is increased (the resistance of insulating 
material and carbon decreases with an increase of 
temperature). To find the resistance of a coppei 






48 TEXT BOOK ON BADIO 


wire, multiply its length in feet by 10.5 and divide 
the product by its area in circular mills. 

A rheostat is constructed of a number of metal coils 
or grids (these coils or grids are made of some metal 
offering high resistance to the flow of current over 
them, generally iron or German silver) connected in 
series, these coils or grids are mounted on a metal 
frame from which they are insulated, the whole thing 
being covered with a perforated metal cover. The 




RHEOSTATS IN SERIES 

Fig. 8 

first and last coil are each connected to a terminal 
which allows for the connection of the conductors 
(see Fig. 6). The current enters the rheostat through 
terminal P, then passes through the coil or grid A 
to B, then to C and so on till it has passed through 
each of the coils in turn and leaves the rheostat 
through terminal S. Most of the rheostats manufac¬ 
tured today are of the adjustable type, so constructed 
that by the turning of an adjustable lever a number 
of the coils can be cut in or out of the circuit, thus 
cutting in or out resistance, thereby lowering or in- 


























RHEOSTATS 


49 


creasing the amperage. Fig. 9 is an elementary draw¬ 
ing showing how this is accomplished. P is the 
terminal through which the current enters the 
rheostat, S the terminal through which it leaves after 
having passed through the series of coils or grids. As 
will be seen by referring to the diagram (Fig. 9) it 
depends on which contact points 1, 2, 3, 4 or 5, the 
adjusting lever N is placed as to the number of coils 



Fig. 9 

through which the current will pass. With the lever 
“N” or contact No. 1 the current will pass through 
coils A B C D only, by turning the lever to contact 


4 




























50 TEXT BOOK ON BADIO 


4, two coils K and L will be cut out of the circuit; 
while if lever is placed on contact 5 the current must 
pass through all the coils or grids before leaving 
through terminal S. 



RHEOSTATS IN MULTIPLE 


* 


Fig. 10 






















TRANSFORMERS 


A transformer is a device for changing the voltage 
and current of an alternating current circuit. 

Transformers are spoken of as Step-up and Step- 
down transformers. 

The three essential parts of a transformer are two 
copper coils, known as the primary and secondary, 
and a laminated iron core. 

The core of the transformer is made up of a num¬ 
ber of thin sheets of annealed iron; these sheets are 
very thin, generally running to one-hundredth part 
of an inch in thickness, the exact thickness depend¬ 
ing upon the frequency of the circuit the transformer 
is to be used on. Each of the sheets is given a coat 
of some insulating compound, so that they are* in¬ 
sulated from each other. The sheets are then built 
one upon the other in the form of a hollow square 
till a core large enough is obtained, the sheets are 
then clamped together and are insulated with mica 
or some other insulating material, so that the two 
copper coils may be wound around the core without 
the copper wire of the coils coming in contact with 
the iron core. Fig. 11 is a diagram of an elementary 
transformer, showing the primary coil wound around 
one leg of the core and the secondary coil wound 
around the opposite leg. 

When we close the circuit on the primary side of 
transformer the current passing through the primary 
coil magnetizes the iron core, this magnetism in turn 
induces an a.c. current in the secondary coil. So 


51 


52 TEXT BOOK ON RADIO 


that while the primary and secondary coil are in¬ 
sulated from the core and from each other, there is 
a magnetic connection between both coils and core. 

If we turn back to the basic principle of induction 
the working principle of the transformer is made 
clear. 

If an a, c, current is passed through a conductor 
encircling a bar of soft iron, the iron will become a 
magnet and remain so just as long as current is 
passed through the conductor. 

If a bar of iron carrying a conductor around it be 
magnetized in a direction at right angles to the plane 
of the conductor a momentary emf will be induced 
in the conductor; if the current be reversed another 
momentary emf. will be induced in the opposite 
direction in the conductor. 

The pressure induced in the secondary coil depends 
on the ratio between the number of turns in the pri¬ 
mary and secondary coils. Suppose the primary coil 
has 100 turns of wire and is connected to a 100 volt 
line, and draws ten amperes, and the secondary coil 
has 50,000 turns of wire, the voltage on the secondary 
side of the transformer will be 50,000 but the amper¬ 
age will be one-fiftieth of an ampere. So we see that 
the wattage on the primary is equal to the wattage 
on the secondary, assuming that there is no loss in 
transformation. 

We know that there are two forms of losses in all 
transformers, the iron or core loss and the copper 
or coil loss. 

All of the magnetic dux due to the current flowing 
in one winding and linked with that winding is not 
also linked with the other winding. The path of a 
certain part of the flux is through the air, outside of 





TRANSFORMERS 


53 


the core. This part of the flux due to one winding 
which is not linked with the other winding is called 
its “leakage” flux. In well-designed transformers 
this leakage flux is quite small. The leakage flux ob¬ 
viously is not effective in transferring energy from 



one winding to the other. Leakage may be reduced 
by offering to the magnetic flux a complete path of 
high permeability. One way to do this is to use a 
closed core, so that the path of the magnetic flux is 
entirely through iron; in the open-core transformer 
part of the path of the magnetic flux is through air, 
and considerable leakage necessarily results. Another 
way is to use a core of large cross-section, so that the 
iron is worked at low flux densities. Leakage is also 
reduced by bringing the coils close together and mak¬ 
ing them approach coincidence. This may be done by 
winding one winding right on top of the other; very 
little magnetic flux can then be linked with one wind¬ 
ing and not with the other. 

The transformer is one of the most efficient kinds 



















54 


TEXT BOOK ON RADIO 


of electrical apparatus. The efficiency of well-de¬ 
signed transformers is usually from about 94 to 98 
per cent, according to size, the larger units being the 
more efficient. There are “copper” losses in primary 
and secondary windings, equal to the resistance times 
the square of the current. There are “eddy current” 
losses due to the currents induced in the iron core. 
If the iron core were solid, currents would be set up 
in the whole cross section of the core in the same 
plane as the plane of a turn of winding. By using 
thin sheets of iron the path of the eddy currents is 
reduced, and hence the eddy-current loss. At com¬ 
paratively low frequencies the eddy-current loss is 
proportional to the square of the frequency and also 
to the square of the thickness of the sheets or lamina¬ 
tions. At radio frequencies other effects must be 
taken into consideration, and these relations do not 
hold. At high frequencies it is important to have 
the laminations as thin as possible. In transformers 
for commercial frequencies the thickness of the lami¬ 
nations is usually between 0.010 inch and 0.030 inch. 
If a solid core were used in a transformer for handling 
any considerable amount of power, enough heat might 
be quickly evolved by the eddy currents in the core 
to destroy the unit. There is also another loss in 
the iron, called the “hysteresis” loss. Hysteresis 
losses are caused by reversals of the magnetism of 
the core and represent the energy required to change 
the positions of the molecules of the iron core. At com¬ 
paratively low frequencies hysteresis losses are di¬ 
rectly proportional to the frequency and are greater 
the higher the flux density at which the iron is worked 
The sum of the eddv-current losses and the hysteresis 
losses is known as the “core losses” or “iron losses.” 








TRANSFORMERS 


55 


The core losses occur as long as a voltage is applied 
to the primary and are nearly the same whether the 
secondary is delivering a load current or not. The 
current taken by the primary when the secondary 
circuit is open supplies these losses in the iron. It 
is therefore very important to design transformers so 
that the eddy-current losses and hysteresis losses are 
small. This is particularly important in transformers 
which are connected to the line all the time but supply 
a load during only a small part of the day, as trans¬ 
formers on electric-light systems, and is less important 
on transformers supplying full load secondary current 
all day, as transformers in a power house. 

The cores of most transformers and other apparatus 
for alternating currents are now made of silicon steel 
instead of soft iron or a mild steel. One advantage 
of silicon steel is that when subjected to heat it does 
not age appreciably; that is, its permeability does not 
decrease with use. Ordinary soft iron will age 
rapidly with heat. Therefore a transformer with 
core of silicon steel can be operated at a higher 
temperature than a transformer with soft-iron core. 
Another important advantage of silicon steel is that 
its ohmic resistivity for electric currents is much 
higher than soft iron, and therefore in a given trans¬ 
former the eddy-current losses will be less with a 
silicon-steel core than with a soft-iron core. The per¬ 
meability of silicon steel is about the same as the 
permeability of the soft iron which has been used 
for transformers. Practically all core transformers 
used for radio apparatus, for either transmitting or 
receiving, have cores made of silicon steel. 

The losses represent electrical energy converted into 
heat. Some means must be provided for dissipating 








56 TEXT BOOK ON BADIO 


this heat, or the temperature of the transformer may 
rise until it is destroyed. Small sizes, including most 
of those found in radio stations of moderate size, may 
be cooled by simply being exposed to the air. The 
exposed surface of the windings must be sufficient to 
dissipate the heat. In larger sizes an air blast may 
be blown through the transformer. Large trans¬ 
formers are also cooled by immersing the windings 
in oil, which is kept cool by circulation. 

If a tap is brought out from an intermediate point 
of the winding of an inductance coil, a part of the 



AMMETER CONNECTED IN SERIES 

Fig 12 

voltage applied at the terminals may be tapped off 
between one terminal and the intermediate tap. This 
can be considered to be a transformer in which one 
winding serves as both primary and secondary. It 
is simple and cheap, but has the disadvantage that the 
two windings are not insulated and the voltage to 
ground of the high-voltage winding also exists in the 
low-voltage circuit. Its use is confined for the most 
part to small sizes. This device is often called an 
‘ ‘ auto-transformer . 9 ’ 









LOSS IN TRANSFORMER 


57 


In radio apparatus the load on the secondary of a 
transformer usually includes a capacity. It may be¬ 
come desirable to adjust the system consisting of the 
a.c. generator, transformer, and secondary condenser 
so that the impedance of the primary circuit is a 
minimum; that is, so that the condition of 
“resonance” exists. This arrangement is called a 
“resonance transformer.” With such an arrange¬ 
ment it is possible to obtain very high voltages. One 
type of transformer employing resonant circuits is 
sometimes called a “Tesla coil” and may be made to 
produce spectacular high-voltage effects. 

On closing the primary switch when a transformer 
is first connected to the line a relatively very large 
current may flow for an instant, its magnitude de¬ 
pending on the state of magnetization in which the 
iron was left when the transformer was last discon¬ 
nected from the line. This momentary current ob¬ 
tained on closing the primary line switch may in some 
cases be perhaps 10 times the primary rated full-load 
current and may blow the fuses in the primary line. 

Transformers used for alternating currents of radio 
frequencies usually have air cores; that is, no iron 
is employed, as has been stated. If an iron core is 
used, very thin laminations are employed. At radio 
frequencies, the effectiveness of iron in increasing the 
magnetic flux is not as great as at low frequencies, 
the eddy currents contributing to this effect. Small 
radio-frequency transformers are used in electron tube 
amplifiers. Small transformers with iron cores, for 
frequencies up to perhaps 3,000, are also employed in 
electron tube amplifiers. 

A common use of a transformer with radio fre¬ 
quencies is to obtain an alternating current from a 











58 TEXT BOOK ON BADIO 


pulsating current. For example, in the use of electron 
tubes for amplifying received signals, pulsations are 
produced in the plate current, above and below its 
normal steady value. By passing the plate current 
through the primary of a transformer, an amplified 
alternating emf. is obtained in the secondary, and 
this emf. is applied to the grid circuit of a second 
electron tube, and so on. 

A reactance coil can be made by constructing a hol¬ 
low coil of wire and sliding an iron core made of sheet 
iron in or out of it according to whatever adjustment 
is required. Number 10 wire is suitable for the coil 
and Number 12 wire for the primary coil. The coil 
is connected in series with the primary windings. 





THE AERIAL 


The aerial is a wire or system of wires strung above 
the surrounding objects and insulated from them and 
connected to a radio set by means of a lead-in wire. 
The same aerial can be used for either sending or 
receiving the electro-magnetic waves. The purpose 
of the aerial is to radiate electro-magnetic waves when 
used as the aerial for a transmitting or broadcasting 
station and to receive or intercept waves when used 
with the receiving set. Practically any sort of wire 
will answer the purposes for a receiving aerial. Cop¬ 
per wire, phosphor bronze, copper clad steel, in fact, 
we have seen used a metal smoke stack, wire netting, 
a tin roof, a metal bed spring and a number of other 
metal objects with varying degrees of success. How¬ 
ever, for maximum results, we suggest that a single 
wire be used for receiving and that wherever possible 
the following dimensions be used: 

Aerial Recommended for Various Wave Lengths . 


Wave Length 
in Meters 

Height from 
Ground in Ft. 

Length of 
Aerial in Ft. 

150 . 

.30. 

.... 75 

200 . 

.50. 

.... 80 

200 . 

.60. 

.... 50 

200 . 

.30. 

.... 90 

250 . 

.40. 

.... 100 

300 . 

.60. 

.... 100 

400 . 

.80. 

.... 130 

500 . 

.60. 

.... 180 

600 . 

......80. 

.... 230 


59 





















60 TEXT BOOK ON RADIO 


Of course, local conditions must be taken into con¬ 
sideration, and probably a little experimenting with 
aerials of different lengths placed at different angles 
will assist to get ideal working conditions. Aeroplane 
wire makes an ideal aerial as it is flexible and easy to 
work with. As for indoor aerials, these are becoming 
more popular every day, and the day is not far off 
when we shall be able to have our receiving set, aerial 
and loud speaker all enclosed in a cabinet no larger 
than our present day victrola. It is my opinion 
that the best indoor aerial is made by winding about 
20 or 30 turns of copper wire on a wood frame about 
2 feet square. However, both outdoor and indoor 
aerials may take a number of shapes and each w T ill 
be found to have its own characteristics and different 
effects will be obtained from different combinations. 

The effectiveness of the antenna system depends 
largely upon the character of the ground connection. 
The most practical ground connection is the water 
supply system. Where this is not available, pipes 
connected with the heating or gas systems may be 
used. The drawback with these pipes, however, is 
that the joints of these pipes are sometimes cemented 
with insulating material. Ground clamps for attach¬ 
ing the ground wire leading from the receiving set 
to the water pipes are obtainable at most dealers and 
electrical supply houses. The water pipes should be 
carefully scraped to remove all paint or corrosion be¬ 
fore attaching clamp. Where the above mentioned 
means of ground connection is not available, wires or 
metal plates may be buried in the earth and connected 
to the apparatus. Such wires or plates should in¬ 
clude an area, of at least 30 square feet. 

A counterpoise consisting of at least the same num- 





GROUND CLAMP 


61 


ber of wires as are used in the antenna may be sus¬ 
pended beneath the antenna and used in place of a 
ground connection for the receiving apparatus. 

There are two general classes of antennas, those 
which act primarily as electrical condensers and those 
which act primarily as electrical inductances. The 


Ground Clamp. 




Fig. 13 


first type is usually referred to simply as an “an¬ 
tenna. ’ ’ The second type is usually referred to as a 
“coil antenna,” “coil aerial,” “loop,” or when used 
for a particular purpose, as a “direction finder. 7 

A simple antenna of the condenser type would con¬ 
sist simply of two parallel metal plates, separated. 
The energy radiated or absorbed by an antenna of 
the condenser type depends on its capacity, and to 
form an antenna of large capacity two metal plates 
















62 


TEXT BOOK ON RADIO 


would have to be so large as to be very expensive and 
cumbersome. 

Instead of using two parallel metal plates, it would 
be possible to form a condenser consisting of one 
metal plate suspended over and parallel to the 
ground, providing the surface of the ground is ap¬ 
preciably conducting. The plate is supported above 
the earth and insulated from it, except for the con¬ 
nection through the wire called the ‘ ‘ lead-in wire, ’ ’ 
or “lead-in.” The plate and the conducting surface 
of the earth form the two plates of a condenser, the 
air between them furnishing the dielectric. The ap¬ 
paratus used for receiving is introduced into the lead- 
in, between the plate and the ground. When radio 
waves reach an antenna they set up an alternating 
emf. between the wires and the ground. When an 
alternating emf. is introduced into the wire, charging 
currents flow into and out of the plate and the earth, 
the dielectric being strained first in one direction and 
then in the other. As has been explained in the 
previous chapter, these strains are equivalent to dis¬ 
placement currents of electricity through the dielec¬ 
tric, which serves to complete the circuit. A region 
in which the dielectric is undergoing alternating 
strains is the starting point of electric waves. The 
larger the plate and the higher it is raised from the 
earth, the greater the amount of space in which this 
strained condition exists, and the more powerful the 
waves which are radiated. 

However, in order to construct with a given amount 
of metal an antenna having the greatest possible ca¬ 
pacity, the metal should not be used in the form of 
a single plate. A much more efficient form consists 
of a number of parallel wires. The antennas found 









AERIALS 


63 


in practice usually consist of arrangements of wires. 
A single vertical wire is, for its size, the best radiator, 
but it has to be made extremely long in order to get 
sufficient capacity for long wave or long distance work. 
Antennas consisting of horizontal or inclined wires 
are, however, also very satisfactory. Any arrange¬ 
ment of wires which will constitute one plate of a 
condenser may be used, although some arrangements 
will radiate and receive much better than others. 

A satisfactory antenna can also be constructed, 
using a suitable arrangement of wires for the upper 
plate of the condenser and using for the lower plate 
a number of parallel wires elevated a few feet from 
the earth and insulated from the earth. No connection 
is then made to the earth itself. The wires forming 
the lower plate of the condenser are then called a 
‘ ‘ counterpoise antenna ’ ’ or simply a ‘ ‘ counterpoise. ’ 

In reception electric waves reaching an antenna set 
up an alternating emf. between the wires forming the 
upper plate of the condenser, and the ground or other 
lower plate of the condenser. The longer and higher 
the wires forming the antenna the greater the emf. 
produced. As a result of this emf. an alternating 
current will flow in the antenna wires. The energy 
of the current is absorbed from the passing wave, 
just as some of the energy of a water wave is used 
up in causing vibrations in a slender reed which 
stands in its way. 

An antenna consisting of horizontal parallel wires 
supported between two masts and insulated therefrom 
is common. This is a standard form for ship stations. 
If the lead-in wires are attached at the end of the 
horizontal wires the antenna is said to be of the in¬ 
verted L type. If the lead-in wires are attached at 





64 TEXT BOOK ON EADIO 


the center of the horizontal wires, the antenna is said 
to be of the T type. Both of these types are found 
at many land stations, including amateur stations. 
The wires are kept apart by “ spreaders, ” which may 
be of wood. These two types are often referred to 
as “flat-top” antennas. 

The V type of antenna consists of two sets of hori¬ 
zontal or slightly inclined wires supported by three 
masts, so that the horizontal portions form an angle. 
The V type is used to some extent in military work, 
but is not much used elsewhere. 

The “fan” or “harp” antenna consists of a num¬ 
ber of wires radiating upwards from a common termi¬ 
nal to various points on a supporting wire to which 
they are connected. The supporting wire is insulated 
at each end from the tower or other support. Prac¬ 
tical advantages of the fan type are that there are 
only two insulators, so that leakage is small, and that 
the mechanical strain to be carried by the supports 
is comparatively small. 

The “cage” type of antenna is used to a consider¬ 
able extent, particularly on ships. A number of 
parallel wires, often six or eight, are supported from 
a single point and are kept apart by star-shaped sep¬ 
arators which may be of wood, or by hoops. 

For transmission over short distances a very simple 
antenna may be used, such as, for example, a single 
wire supported between two stakes at a height of only 
a few feet from the ground. In some cases a long in¬ 
sulated wire may be laid upon the ground or in a 
shallow trench, forming a “ground antenna.” For 
receiving stations equipped with good electron tube 
amplifiers very simple antennas may be employed, 
even for long-distance work, such as a single sus¬ 
pended wire, a ground antenna, or a coil antenna. 





AERIALS 


65 


The umbrella type of antenna consists of a number 
of wires which diverge from the top of a mast, and 
are attached to anchors in the ground through in¬ 
sulators. 

When an emf. is introduced into an antenna, a 


T A£fl/AL 



charging current flows in the wires. If we attempt 
to form a picture of this process in the wire antenna, 
we must remember that every inch of the wire forms 
a little condenser, with the earth acting as the other 
plate. The antenna is said to have a distributed 
capacity. 

As the electricity flows from the bottom of the an¬ 
tenna, some of it accumulates on each portion of the. 
wire, causing a displacement current through the 
dielectric to earth. The current in the wire accord¬ 
ingly diminishes as the free end of the antenna is 
approached, and becomes zero at that end. The cur- 

5 




























66 TEXT BOOK ON BADIO 


rent is evidently different at different parts of the 
antenna, being zero at the free end and a maximum 
where the antenna is connected to the ground. This 
is in marked contrast to the case of a direct current, 
which always has the same value at every point of the 
circuit. The difference here is brought about by the 
very high frequency of the currents. 

The voltage of the antenna, on the contrary, is zero 
at the grounded end and has a maximum value at the 
free end. In fact, the latter is the point where the 
most intense sparks can be drawn off; therefore the 
insulation of the antenna from near-by objects and 
the earth must be particularly good at this point. 

A large capacity to earth, concentrated at any point 
of the antenna, causes a large change in the current 
at that part of the antenna. If this bunched capacity 
is located at the top of the antenna, such as is the 
case with a flat-topped antenna of long wires, with 
only a few vertical lead-in wires, the average current 
in the flat top portion will be large, and it increases 
slightly in strength as 'the charges pass down through 
the lead-in wire (picking up the charges there), hence 
giving a large current through the receiving ap¬ 
paratus. It is a distinct advantage to have as large a 
part of the total capacity of the antenna as possible 
at the t jp. 

The wave length of the waves emitted by an an¬ 
tenna. when no added inductance or capacity is in¬ 
serted in the antenna circuit, is known as its ‘‘fun¬ 
damental wave length.” By putting inductance coils 
(“loading coils”) in the antenna circuit, longer waves 
may be radiated, while on the contrary, condensers 
put in series with the antenna enable it to produce 
shorter waves than the fundamental. The use of a 





AERIALS 


67 


series condenser is avoided where possible, since it has 
the effect of decreasing the total capacity of the an¬ 
tenna circuit and thereby diminishing the amount of 
power which can be given to the antenna. The addi¬ 
tion of some inductance has a beneficial effect, since 
the decrement of the antenna is thereby lessened and 
a sharper wave results. It is not advisable to load 
the antenna with a very great inductance, however, 
as it is not an efficient radiator of waves. The waves 
emitted are very much longer than the fundamental 
wave length. As a general rule small sending stations, 
for short ranges, work best on short waves, and long¬ 
distance stations on long waves. Long waves have 
the advantage for long distance work that they are 
not absorbed in traveling long distances to the extent 
that short waves are. 

The United States radio laws at present provide 
that every commercial radio station shall be required 
to designate a certain definite wave length as its 
normal transmitting and receiving wave length, and 
that this wave length must not exceed 600 meters 
or must be longer than 1600 meters. Ship stations 
must be equipped to transmit on either 300 or 600 
meters. Amateur stations must not transmit on a 
wave length exceeding 200 meters. It is probable 
that the radio laws will be revised in the immediate 
future. 

Communication with ships is usually carried on 
with a wave length of about 600 meters. Radio com¬ 
pass stations on shore operate on 800 meters, and 
radio beacon stations on shore, which transmit to ships 
to enable the navigator on the ship to determine its 
position, usually operate on 1000 meters. Most high- 
power stations, such as those for transatlantic work, 





68 


TEXT BOOK ON RADIO 


operate on a wave length of at least 2500 meters, 
usually considerably more. The Annapolis station, 
for instance, operates on about 16,900 meters and the 
New Brunswick station on about 13,600 meters. 

For a simple vertical wire grounded antenna the 
fundamental wave length is slightly greater than four 
times the length of the wire. The constant is often 
used as 4.2, and applies approximately also to flat 
top antennas (L or T types) with vertical lead-in 
wire, the total length being measured from the trans¬ 
mitting apparatus up the lead-in wire and over to 
the end of the flat top. It is usually easier, and cer¬ 
tainly more accurate, to measure the wave length 
radiated from an antenna directly by the use of a 
wavemeter. The wavemeter coil needs merely to be 
brought somewhere near the antenna or lead-in wire 
and the condenser of the wavemeter adjusted to give 
maximum current in the wavemeter indicator. The 
wave length corresponding to the wavemeter setting 
is then the length of the waves radiated by the an¬ 
tenna. The “ fundamental ” wave length of the 
antenna may be determined by gradually decreasing 
the number of turns in the loading coil, measuring 
the wave length for each setting of the loading coil, 
and plotting a curve showing the wave length corre¬ 
sponding to the various numbers of turns of the load¬ 
ing coil. The “ fundamental ” is the wave length cor¬ 
responding to zero turns, and corresponds to the point 
where the extension of the curve cuts the wave length 
axis. 

The amateur is required by law to transmit on a 
wave length not exceeding 200 meters and is interested 
to know the kind of antenna to use. It is impossible 
to give an exact rule for constructing an antenna for 







AERIALS 


69 


a particular wave length, because many local condi¬ 
tions peculiar to each case must receive consideration. 
An approximate rule which will be found convenient 
in constructing an antenna which is to transmit on a 
wave length not exceeding 200 meters is that the 
over-all length of the circuit from the ground connec¬ 
tion through the entire path which the current follows 
to the end of the antenna must not exceed 120 feet. 
This distance, 120 feet, includes the distance from 
ground up the ground lead to the antenna switch, 
from the antenna switch to the oscillation transformer 
and back to the antenna switch, through the antenna 
lead-in to the antenna top, and along the antenna top 
to its end. This approximate rule applies to the 
various types of antennas ordinarily found at amateur 
stations, including inverted L, T, and fans. In the 
case of an antenna, for which the lead-in is taken 
off the antenna top at an intermediate point, as in a 
T antenna, the distance along the antenna top should 
be measured to the most distant end of the top, if the 
lead-in is not connected at the middle of the top. If 
an antenna is constructed in which the distance meas¬ 
ured as described does not exceed 120 feet, it is prob¬ 
able that with suitable transmitting apparatus and no 
loading it will be possible to transmit on less than 200 
meters, but if loading inductances are used or equiva 
lent changes made in the transmitting apparatus the 
emitted wave length may, of course, considerably ex¬ 
ceed 200 meters. 

It is a familiar fact that devices for transmitting 
or receiving wave motion of any kind, which are not 
symmetrical with respect to a line perpendicular to 
the plane in which the wave travels, will transmit and 
receive better in one direction than in another. Thus 





70 


TEXT BOOK ON RADIO 


a resonator for receiving sound from a distance 
should be turned perpendicular to the direction of 
the source of the sound, to give the maximum response. 

A single vertical wire forms an antenna which is 
entirely symmetrical for radio waves traveling hori¬ 
zontally, and such a wire has no directional effect. If 
for a given antenna fixed in a given position we plot 
a curve showing the strength of the received current 
received from transmitting stations located in differ* 
ent directions, we will find this curve a very useful 
means of describing the directional characteristics of 
the antenna. For the single vertical wire the direc¬ 
tional characteristic is simply a circle drawn with the 
foot of the wire as center. Most of the other types of 
antennas ordinarily used have directional properties, 
at least to some extent. The inverted L antenna has 
a considerable directional effect. An inverted L an¬ 
tenna with a long, low top such as are often found 
at large stations, has a marked directional effect. The 
length of the line drawn from the central point A in 
any direction indicates the strength of the current 
received from a transmitting station located in that 
direction. It will be noted that the inverted L trans¬ 
mits and receives best in the direction opposite to that 
in which the antenna top points. Ground antennas 
have marked directional characteristics. The most 
important type of directional antenna is, however, the 
coil antenna. Particular kinds of directional effects 
can be secured by combining different kinds of di¬ 
rectional antennas. 

The directional properties are most often made use 
of for receiving, but are also used for transmitting. 

In transmitting, a considerable part of the energy 
may be concentrated in a particular direction by the 








AERIALS 


71 


use of a directional antenna, and the range of a 
transmitting station thus increased and interference 
decreased. Directive transmission may also be very 
helpful to a ship or airplane in aiding it to determine 
its location. 

In receiving; an antenna having a marked direc¬ 
tional characteristic, such as a coil antenna, will re¬ 
ceive strong signals from a particular direction, and 
weaker signals from other directions. This is valu¬ 
able in reducing interference from stations which it 
is not desired to receive, since in general the interfer- 



Fig. 15 

ing station is not likely to lie in the same direction as 
the station which it is desired to receive. 

Antenna Construction 

For land stations wooden masts have been much 
employed. For portable antennas these are made in 
sections, which fit together like a fishing rod. For 
higher-power stations latticed metal masts are com¬ 
mon and in some cases tubular metal masts in tele¬ 
scoping sections. Except in special instances, guy 
ropes or wires are necessary, and in some cases the 
support is sustained entirely by these. It has been 
quite generally regarded as a structural advantage to 















72 


TEXT BOOK ON RADIO 


allow a small freedom of movement to the mast, so 
that it may rock slightly in the wind. A simple one- 
wire antenna may be held by any support that is avail¬ 
able. When a tree is used to support either end, a 
rope should run out for some distance from the tree 
and the wire be attached to this by an insulator, so 
that the antenna w 7 ire itself may not be in or near 
the tree. The standard flat-top ship antenna makes 
use of the ship’s masts for supports. The antenna 
wires are stretched between two booms or spreaders, 
from which halyards run to the masts. 

The insulation of an antenna is a matter requiring 
careful attention. If an insulator is defective or dirty 
or wet, the energy radiated from the antenna will be 
considerably reduced. Defects of insulators may be 
caused by breakage after installation or faulty manu¬ 
facture, such as small cracks or other openings 
through which the insulator may absorb water, or 
nonuniformity of the material of the insulator. Dirty 
insulators are likely to be found near industrial 
plants, and on ships wet or salt-covered insulators 
may cause trouble. Porcelain is one of the most sat¬ 
isfactory materials for use in constructing insulators 
because of the large voltages which it will stand with¬ 
out failure, but it is not suitable for use under severe 
mechanical vibration. Antenna insulators are often 
made of compositions, such as the material called 
“electrose, ” which is made with a shellac binder. 
These insulators are made in various shapes, including 
rods, and usually have eyebolts or other metal pieces 
molded in. Insulators are also made with ribs or 
petticoats, the purpose of the ribs is to lengthen the 
leakage path which the current must follow between 
eyebolts and to secure better insulation when the in- 





CONSTRUCTION OF AERIALS 


73 


sulator is wet by collecting the water on the lowest 
points of the ribs. In the case of antennas for land 
stations, wire guys are interrupted by “strain” in¬ 
sulators to prevent the guy from having a natural- 
wave length approximately the same as the wave 
length of the antenna. 

Where the lead-in wires from the antenna pass 
through the walls of the house in which the sending 
and receiving apparatus is installed, special care needs 
to be taken to ensure good insulation. In the case 
of some large aerials, the supporting mast itself has 
to be insulated from the ground at its base. The 
design of an insulator which combines sufficient me¬ 
chanical strength with good dielectric properties is a 
difficult matter. 

An antenna switch is a necessity in all permanent 
installations. This has the function of disconnecting 
the receiving apparatus from the antenna completely 
when a message is to be sent, and vice versa. The 
action of such a switch is made such that it is im¬ 
possible for the operator to make a mistake and im¬ 
press the large sending voltage upon the delicate re¬ 
ceiving apparatus. 

Every radio station should be provided with a light¬ 
ning switch on the outside of the building by means 
of which the antenna should be grounded at all times 
when not in use to avoid possible damage from light¬ 
ning. 

Antenna wire .—Desirable qualities in a metal to be 
used for antenna wire are that it shall not be brittle, 
that it shall be durable when exposed to weather and 
other conditions met in service, that its weight shall 
not be excessive, that its cost shall be reasonable, and 
that its ohmic resistance shall be low. It is also some- 







74 TEXT BOOK ON RADIO 


times important that a metal used for antenna wire 
shall possess high tensile strength; this is obviously 
most important for large antennas of long span. 

Hard-drawn copper wire is often used, but has the 
disadvantage that it is brittle and kinks easily. 
Tinned copper wire is sometimes used. Soft-drawn 
copper wire may also be used, depending on the tensile 
strength required for the distance to be covered. 
Aluminum wire is also used, and is satisfactory if 
careful attention is given to the connections and joints, 
to avoid corrosion. An important advantage of 
aluminum wire is that it is light. This is particularly 
important in large antennas, which cover long dis¬ 
tances. 

Iron or steel wire which has been heavily galva¬ 
nized is also used. Since the current flows largely in 
the zinc coating, the resistance is much less than that 
of an ungalvanized steel wire. Steel wire to which 
a thick coating of copper has been permanently 
welded, is sometimes used. The resistance losses in 
the coated steel wires are about the same as in solid 
copper wire, provided that the coated steel conductors 
are not too close together. 

Bare, uninsulated wires are in general use. In some 
cases the antenna wire is covered with a thin coating 
of enamel, whose purpose is to eliminate corrosion of 
the wire by exposure to the weather, smoke, or acid 
or other fumes. 

Solid copper or other conductor, in sizes such as 
No. 14, is often used. Stranded conductor, however, 
has advantages, including flexibility, and lower resist- 
tance at high frequencies than solid conductor, be¬ 
cause of the skin effect. In the stranded conductor for 
a given weight of copper there is much more cross- 





AERIAL WIRE 


75 


sectional area available for carrying the current than 
there is in the solid conductor. The individual strands 
should, however, always be enameled in stranded wire 



used for radio-frequency currents, or the stranded 
conductor may have a higher resistance than solid 
conductor of the same weight. 

An antenna conductor composed of seven or 


















76 


TEXT BOOK ON RADIO 


more strands of carefully enameled No. 22 copper wire 
is usually found to give good satisfaction. Antennas 
of unenameled solid conductor, which are very satis¬ 
factory on the day they are installed, after exposure 
for even a week to the weather, often show a very con¬ 
siderable increase of resistance. Phosphor-bronze 
stranded wire of seven or more strands is sometimes 
used, has a high tensile strength, but is open to the 
objections that it is relatively very expensive, and has 
a comparatively high ohmic resistance. Phosphor- 
bronze wire corrodes easily when exposed to weather, 
and when corroded is very likely to have higher resist¬ 
ance than a solid conductor. A silicon bronze wire is 
now being used to some extent, which does not corrode 
easily, has comparatively low ohmic resistance, high 
tensile strength, and has been found very satisfactory. 
For many ordinary antennas, hard-drawn solid copper 
wire, carefully enameled, will be found most conveni¬ 
ent, and will give good satisfaction. 

To obtain a good conducting ground connection is 
a comparatively easy matter for a ship station. In a 
steel ship a wire is attached to the hull of the ship 
and the good conductivity of the sea water assures 
an intimate connection with the ground. A usual 
method of grounding on a wooden ship propelled by 
steam is to connect the ground lead to the thrust 
box and depend on the propeller to make contact with 
the water. The hulls of some wooden ships are pro¬ 
tected by being covered with copper sheathing, and a 
good ground connection may be made to this sheath¬ 
ing. In some cases a ground for a wooden ship may 
be made by means of a large metal plate attached to 
the outside of the ship, under water. 

The ground connections for a land station should 






AERIAL WIRE 


77 


be designed with the idea of constructing one plate 
of a condenser of which the antenna is the upper 
plate. The area covered by the ground connections 
should be several times the area of the antenna, and 
should be laid out fairly symmetrically with respect 
to the antenna. The effort should be made to obtain 
a considerable number of points of contact with the 
earth, having paths of low resistance. Metal plates 
buried in the earth are often used. A good ground 
system may be constructed by burying metal plates 
of the same area, symmetrically arranged around the 
circumference of a circle having the station as the 
center, and connected to the station by wires sus¬ 
pended a short distance above the earth. A good 
general principle to follow is that the same current 
should be carried per unit area by each buried plate. 
If this principle is not observed, as in a ground system 
laid out at random consisting of a number of ground 
connections of different impedances located at varying 
distances from the station, it may be found that the 
over-all resistance of the system will be considerably 
greater than the resistance of the best one of the 
ground connections used alone. A considerable num¬ 
ber of copper wires run radially from the foot of the 
antenna to a distance considerably greater than the 
length of the antenna will make a good ground if 
the earth is moist. When radial wires are used it is 
often found advantageous to run the wires for a 
short distance suspended above the ground before 
burying them. In dry localities a ground connection 
is sometimes made to a well; this may be found useful 
for receiving, but in general is not very satisfactory. 
In cities a ground connection may be made to water 
pipes or gas pipes. Connections to steam pipes and 







78 


TEXT BOOK ON RADIO 


sometimes to gas pipes may be unsatisfactory because 
they may make poor contact with the ground. Con¬ 
nections to gas pipes should always be made between 
the meter and the street. 

The counterpoise should be designed with the idea 
of constructing the lower plate of a condenser of 
which the antenna is the upper plate, and should 
cover an area at least as great as that of the antenna, 
and preferably somewhat greater. The counterpoise 
may consist of an arrangement of parallel or of radial 
wires, supported 3 or 4 feet above the surface of the 
ground and insulated from the ground. Metal screen 
may also be used. A counterpoise should be supported 
at as few points as possible to keep its resistance low. 
To construct an antenna system of low resistance it 
is necessary to take all precautions to keep low the 
resistance of the condenser constituting the antenna. 
Only-those insulating materials should be allowed in 
the field of the counterpoise which have little dielec¬ 
tric power loss. Wooden stakes should be kept out of 
the field of the counterpoise, because wood usually has 
a considerable power loss. Porcelain insulators are 
usually satisfactory. The counterpoise should be care¬ 
fully insulated from any wooden stakes which sup¬ 
port it by suitable insulators. If used for transmis¬ 
sion with continuous waves, a counterpoise should be 
rigidly supported so that it will not sway with the 
wind in order to prevent variations in the transmitted 
wave length. 

Coil Antennas 

The ordinary elevated antenna acts primarily as an 
electrical condenser, while the coil antenna can be 
considered to act primarily as an electrical inductance. 








GEOUNDS 


79 


A coil antenna consists essentially of one or more 
turns of wire, forming a simple inductance coil. 

In both types of antennas, an approaching radio 
wave induces an emf. in a wire or arrangement of 
wires. In the ordinary elevated antenna the induced 
emf. causes a current to flow in a circuit which in¬ 
cludes a condenser consisting of the antenna and 
ground, or antenna and counterpoise. In the coil 
antenna the induced emf. causes a current to flow in 
a circuit connected to the detecting apparatus which 
is completely metallic. 

It is a common experience in radio stations to be 
able to hear signals on a sensitive receiving set when 
the antenna is entirely disconnected from the set. 
This is largely due to the action of the wiring of 
the set as a coil antenna. 

A common type of coil antenna consists of four 
turns of copper wire wound on a square wooden 
frame about 4 feet on a side. The amount of energy 
received on such a coil antenna is far less than that 
received on any of the ordinary elevated types of 
antennas as practically used. 

It can not be emphasized too strongly that satisfac¬ 
tory results can not be expected in reception using 
coil antennas unless very good electron tubes ampli¬ 
fiers are used to amplify many times the feeble cur¬ 
rent received in the coil. Usually a six-stage amplifier 
is used for satisfactory results, but even with two 
stages of audio-frequency amplification, some signals 
can be received from nearby stations. 

The practical development of the coil antenna and 
its present widespread applications are due entirely 
to the development of the electron tube amplifier to a 
high state of perfection. 





80 


TEXT BOOK ON BADIO 


Coil antennas may be used for either transmission 
or reception, but their use for transmission is rather 
limited, while their use for reception is extensive and 
constantly increasing. 

A coil antenna may be used with satisfactory results 
inside an ordinary building. With suitable amplifi¬ 
cation a comparatively small coil can be used for re¬ 
ceiving transatlantic stations. 

Coil antennas are particularly used when a com¬ 
pact, portable, type of antenna is desired, or when 
an antenna having a marked directional characteristic 
is desired. 

The action of the coil antenna can be considered 
from different points of view. We can imagine two 
vertical wires of the same length, say 300 meters 
apart, supported by and insulated from any con¬ 
venient supports, with their lower ends also insulated. 
Then any radio wave approaching the two wires will 
induce an emf. in each wire. If the wave approaches 
from a direction perpendicular to the plane of the 
two wires, the crest of the wave will reach each of 
the wires at the same instant and the two induced 
emf.’s will be exactly in phase. If the wave ap¬ 
proaches from any other direction, the induced emf. ’s 
will in general be out of phase, and for a given wave 
length the difference of phase will be greatest for a 
wave approaching in the direction of the plane of the 
two wires. If we assume a wave approaching from 
the direction of the plane of the two wires and having 
a wave length of 600 meters, the emf. ’s induced in 
the two wires will be 180° out of phase, because the 
time required for the wave to travel the distance of 
300 meters between the two wires will be one one-mil¬ 
lionth of a second, or one-half the time required for 





COIL AERIALS 


81 


the wave to pass a given point. Hence the emf. at 
the lower end of one wire will have a positive maxi¬ 
mum when the emf. at the lower end of the other 
wire has a negative maximum. If now the upper 
ends of the two wires are connected and receiving ap¬ 
paratus is connected across the lower ends of the 
two vertical wires, a current will flow in the rec¬ 
tangular circuit so formed and can be detected in the 
usual manner. The horizontal wires contribute noth¬ 
ing to the effective emf. in the coil circuit. 

However, for a wave approaching from a direction 
perpendicular to the plane of the two coils the emf.’s 
induced in the two vertical wires will be exactly in 
phase, and the emf. at the lower end of one vertical 
wire will reach a maximum at the same instant as the 



emf. at the lower end of the other vertical wire, and 
no current will flow in the rectangular circuit. 

A similar explanation will obtain for a wave length 
other than twice the distance between the two vertical 
wires. For a given wave length the maximum instan¬ 
taneous potential difference will exist across the lower 
ends of the two wires for a wave approaching in the 
direction of the plane of the two wires, and no po¬ 
tential difference will exist for a wave approaching 
perpendicular to this direction. 

The rectangular circuit, consisting of the two verti¬ 
cal wires and the two horizontal cross connections, of 
6 






















82 


TEXT BOOK ON RADIO 


course constitutes a coil antenna. Coils consisting of 
two or more turns of wire can be regarded as equiva¬ 
lent to vertical antennas of two or more times the 
height of the side of the coil. 

Another way of regarding the action of the coil 
antenna is to consider it as an inductance coil which 
is threaded by the magnetic field of varying intensity 
which is associated with a radio wave. This varying 
magnetic field is at right angles to the direction of 
travel of the wave, and it is horizontal. When the 
wave is traveling in the plane of the coil, the maximum 
number of lines of magnetic force are linked with 
the coil. When the wave is traveling in a direction 
perpendicular to the plane of the coil, no lines of 
magnetic force are linked with the coil and no emf. 
is induced in the coil. 

It is obvious that if the coil is mounted on a frame 
which can be rotated about a vertical axis, then for 
a wave approaching from a given direction the posi¬ 
tion of the coil can be adjusted so that zero signal 
will be obtained in receiving apparatus connected in 
the coil circuit. The adjustment of the position of 
a coil for zero signal is analogous to the adjustment 
of the arms of a Wheatstone bridge to obtain zero 
current in the galvanometer or other detecting ap¬ 
paratus used with the bridge. 

The turns of a coil antenna possess a distributed 
capacity of their own, and the coil has a natural or 
fundamental wave length of its own. The funda¬ 
mental wave length of a coil antenna is the wave 
length which is radiated by the coil when oscillating 
freely by itself without being loaded with any other 
capacity or inductance. As a guiding rule, it may 
be stated that a coil antenna should not be used to 






COIL AERIALS 


83 


receive waves which are shorter than about two or 
three times its fundamental wave length. However, 
when not used for direction-finder purposes, very 
satisfactory results can be obtained by using a coil 
near its natural wave length. That is, to receive short 
waves a coil of small inductance and small distributed 
capacity should be used. Such a coil must have few 
turns. To receive longer waves, coils of a larger 
number of turns may be used. Experience shows that 
best results are obtained with one or two turns em¬ 
bracing a large area for use with short waves, and 
for long w 7 aves coils with 20 to 30 turns, or even 
100 turns, not so large in area. 

It is, of course, desirable to make the received cur¬ 
rent as large as possible. It is found that in a coil 
antenna turned in the direction of the approaching 
waves the received current is greater, the larger the 
number of turns of wire on the coil, the greater the 
area of the coil and the greater its inductance. The 
current varies directly as the area, directly as the 
number of turns, inversely as the resistance, and in¬ 
versely as the wave length of the wave which is being 
received. 

It would seem at first sight that the increase in re¬ 
sistance due to increasing the number of turns and 
their area would be offset by the rapid increase of 
the inductance with the number of turns and the area 
of the coil. The resistance to high-frequency cur¬ 
rents is, however, dependent on the wave length and 
increases rapidly as the latter approaches the value 
of the fundamental wave length of the coil. 

For convenience of construction square coils are 
found to be the most suitable. The wire may be 
wound in a flat spiral or on the surface of a square 





84 


TEXT BOOK ON RADIO 


frame. With flat spirals only a few turns are used, 
since the inner turns rapidly become less useful as 
the area diminishes. The spiral type of coil is com¬ 
paratively little used in the United States. 

The usual type of coil antenna consists of one or 
more turns of wire wound on a square or rectangular 
frame. One or two turns of copper wdre wound on 
a simple wooden frame 3 or 4 feet square will make 
a simple coil w T hich will be suitable for some pur¬ 
poses. For indoor use for all ordinary purposes the 
wire used for a coil antenna may be No. 20 or No. 22 
ordinary insulated copper wire, with solid conductor. 

The spacing of the turns of a coil depends on the 
allowable capacity of the coil. Spacings of one-half 
inch and 1 inch are common; a spacing of one-quarter 
inch is also used sometimes. 

The capacity of a coil of given dimensions increases 
with the number of turns, at first rapidly, and then 
more slowly. With the wires close together, the ca¬ 
pacity is a maximum and grows rapidly less when 
the wires are separated, until a certain critical spac¬ 
ing is reached, beyond which the capacity changes 
very slowly. 

For a square coil 8 feet on a side the wires should 
be placed at least 0.35 inch apart; for one 4 feet 
square, 0.2 inch; and for a 2-foot coil, one-eighth inch. 
Increasing the distance between the wires decreases 
the inductance of the coil; at the same time it reduces 
the capacity. However, it is found that, for a given 
length of wire, properly spaced as just indicated, the 
fundamental wave length of the coil is about the 
same with different, dimensions. This fact is illus¬ 
trated in the following table, where 96 feet of wire 
are used in each case. 






COIL AERIALS 


85 


Characteristics of coil antennas 


Length 
of a side 
of the 
square 
(feet). 

Number 

of 

turns. 

Spacing 

of 

wire 

(inch). 

Inductance 

(micro¬ 

henries). 

Capacity 

micro¬ 

farads. 

Funda¬ 

mental 

wave 

length 

(meters). 

8 

3 

% 

96 

75 

160 

6 

4 

y 4 

124 

66 

170 

4 

6 

% 

154 

55 

174 

3 

8 

Vs 

193 

49 

183 


These coils should be used with a condenser of 
sufficient capacity to bring them into resonance at 
500 to 600 meters. The first coil would be most suit¬ 
able for these wave lengths on account of its small 
high-frequency resistance and greater effective area. 

The following observations, taken on actual coils, 
show the effective wave-length ranges of different 
types of construction for a given capacity of tuning 
condenser, connected directly across the coil termi¬ 
nals. 

Coil, 5 feet square, spacing of turns in each case, 
one-half inch. Using variable condenser having maxi¬ 
mum capacity 0.00065 microfarad, minimum capacity 
0.00004 microfarad. 

With 4 turns.. . a=200 to 400 meters. 

With 8 turns. A=350 to 700 meters. 

With 16 turns. A=500 to 1000 meters. 

Coil, 5 feet square. Spacing of turns, one-half inch. 
Using variable condenser having maximum capacity 
0.00140 microfarad, minimum 0.000045 microfarad. 

With 4 turns. A=380 to 650 meters. 

With 8 turns. A=400 to 950 meters. 

With 16 turns. A=675 to 2300 meters. 

Coil, 4 feet square. Four turns, spaced 1 inch. 

Using variable condenser having maximum capacity 


























86 


TEXT BOOK ON BADIO 


0.00140 microfarad, minimum 0.000045 microfarad 
A=180 to 500 meters. 

Coil, 4 feet square. Four turns, spaced 1 inch. 
Using variable condenser having maximum capacity 
0.00060 microfarad, minimum 0.00004 microfarad 
A=150 to 350 meters. 

The distance over which coil antennas can be used 


1 


Loop 

AERIAL. 








‘To Neiff 
op 

Ahpupieb 


Fig. 18 
































COIL AERIALS 


87 


for the reception of field transmitting sets is, of course, 
short. When used to receive high-power stations, 
however, very good results may be obtained. With 
good amplification the high-power European stations 
can be heard in Washington, using coil antennas such 
as have been described. An instance is on record 
where all the great European stations were received 
in France on a coil only 18 centimeters square, having 
200 turns. On a coil 10 inches in diameter signals 
have been received in Paris from the arc station at 
Annapolis. 

The name “resonance wave coil” has been applied 
to a coil antenna consisting of a large number of 
turns of very fine wire wound on a tube a few inches 
in diameter. When one terminal of such a coil is 
connected to ground and the other end left free, and 
a turn or two of wire coupled to the coil and con¬ 
nected to the input of a gcod amplifier, signals can 
be received from a considerable distance. Such a 
device, however, does not act entirely as a coil an¬ 
tenna. 

It is not necessary that a coil antenna be entirely 
insulated from ground, although this is desirable. 
Signals can be received with a single-turn coil having 
the lower cross connection completed through the 
ground. Thus, in a large building having two per¬ 
pendicular pipes, perhaps 30 feet or more long and a 
similar distance apart, running direct from the ground 
up above the roof, a workable single-turn coil antenna 
can be constructed by simply connecting the upper 
ends of the pipes by a wire and inserting the receiving 
apparatus in the middle of the wire. The current 
flows from the top of one pipe down that pipe, through 
the ground, up the other pipe, and across the connect- 





88 TEXT BOOK ON RADIO 


ing wire through the receiving apparatus to the top 
of the first pipe. Good results have been obtained 
with such a single turn coil, and it has been found to 
have well-marked directional properties. Since it is 
always grounded, it is at all times protected against 
lightning. If it is not convenient to locate the receiv¬ 
ing apparatus on the top floor of the building, a pair 
of wires may be tapped in on the upper connecting 
wire and run down to a lower floor. On account of 
the large size of a loop of this kind it is not well 
adapted for the reception of waves less than about 
1000 meters in length, the effective working wave 
length range of a particular loop depending of course 
on its dimensions. 

Aerial Outfit 

The Westinghouse Electric & Manufacturing Com¬ 
pany have provided a standard aerial outfit which is 
ideal for amateur and broadcasting reception. It is 
especially well adapted to use with their sets. The 
outfit consists of 150 feet of No. 14 Copper Weld 
Wire, one Splicer, two Micarta Aerial insulators, 



Fig. 19—Westinghouse Complete Aerial Outfit 









WESTINGHOUSE AERIAL 89 


two Screw Eyes, three Porcelain Knobs with holding 
screws, one Porcelain Wall Tube, 50 feet of insulated 
Ground Wire, one Ground Clamp and one Receiving 
Aerial Protective Device. 

The Aerial Protective Device consists of a carefully 
maintained safety gap and a fuse protector. The 
safety gap is so set and the value of the fuse such as 
to assure protection from lightning and power lines. 


S 



i 






COUPLED CIRCUITS 


When two circuits have some part in common or 
are linked together through a magnetic or an electro¬ 
static field they are said to be “ coupled. ” If two 
circuits have an inductance coil in common their re¬ 
lation is said to be “direct inductive coupling.” If 
they have a condenser in common, their relation is said 
to be “direct capacitive coupling.” If they have a 
resistance in common, their relation is said to be “re¬ 
sistance coupling.” If two circuits are mutually in- 


ssv 


/W9\__ 

L.b. 


Cl 


CZ 


Fig. 20—Direct Coupling 


ductive and have no part in common other than the 
mutual inductance, their relation is said to be “indi¬ 
rect inductive coupling,” usually called simply “in¬ 
ductive coupling.” Sometimes the coupling is modi¬ 
fied by using two additional condensers. Each circuit 
contains two condensers in series and one condenser 
in the first circuit is coupled to one condenser in the 

90 










CAPACITIVE COUPLING 


91 


second circuit through a coupling condenser; this is 
described as “indirect capacitive coupling." Mutual 
inductive coupling is used very extensively in con¬ 
structing radio apparatus. It often happens that the 
two coils constituting a mutual inductance are so 
mounted that they also constitute the two plates of a 
condenser whose capacitive reactance is appreciable 



Fig. 21—Inductive Coupling 


at radio frequencies, and in this case the effect of the 
coupled coils is a combination of inductive coupling 
and capacitive coupling. 

It is customary to denote as the “primary’' that 
circuit in which the applied emf. is found, the 
other being regarded as the “secondary" circuit. 
When two circuits are coupled they react on one an¬ 
other so that the current in each circuit is not the 
same as would be the case were the other circuit 
absent. The extent of the reaction is, however, very 
different in different cases. Circuits are said to be 
“closely coupled" when any change in the current in 
one is able to produce considerable effects in the other. 
When either circuit is little affected by the other the 

















92 TEXT BOOK ON RADIO 



LI 


coupling is regarded as “loose.” The coupling be¬ 
tween two inductively coupled circuits is changed by 
changing the distance between the two coupling coils. 
In general, increasing the distance between the two 
coils will make the coupling looser, providing each coil 
is moved parallel to its original position. If the dis¬ 
tance between the two coils is not changed, but they 
are moved so that the angle between their projected 
axes is changed, the coupling will also be made looser, 
since fewer lines of force are then linked with both 
coils. 



Fig. 23—Binding Posts 



















DAMPING 


Thus far it has been assumed that a constant alter¬ 
nating voltage has been applied to radio circuits, in 
which case the alternating currents produced are of 
constant amplitude. Such currents may be regarded 
as analogous to the forced oscillations which are pro¬ 
duced in a mechanical system like a swing or a 
pendulum, when it is acted upon by a force which 
varies periodically. The system is forced to vibrate 
with the same frequency as that of the force. 

It is, however, possible to produce oscillations of 



Fig. 24—Effect of Distributed Capacity in the Unused 

Turns of a Coil 

current in a circuit without the necessity of providing 
a source of alternating emf. A common method is 
merely to charge a condenser and then to allow it 
to discharge through a simple radio circuit. 

93 









94 TEXT BOOK ON RADIO 


This may be accomplished, for example, by the 
simple means shown in Fig. 25. By throwing the 
switch S to the left, the condenser C is charged by the 
battery E, but when the switch is thrown to the right, 
it is discharged into the circuit containing the resist¬ 
ance R and the inductance L. If the resistance R 
is not too great, electric oscillations are set up which, 
however, steadily die away as their energy is dissi¬ 
pated in heat in the resistance. 

To explain this action, we must follow more closely 
what takes place in the circuit from the moment when 
the condenser, charged up to a certain potential dif¬ 
ference, is inserted in the discharge circuit. When the 



condenser starts to discharge itself, a current flows 
out of it, and the potential difference of the plates 
decreases as a result. At the moment when the plates 
have reached the same potential, current is still flow¬ 
ing out of the condenser. The current has energy and 
can not be stopped instantly. In fact, to bring the 













DAMPING 


95 


current to zero value it is necessary to oppose it by 
an emf., and the amount of emf. necessary is greater 
the more quickly one wishes to stop the current. It 
is similar to the case of a moving body. On account 
of its motion the body possesses energy, and can not 
be brought to rest instantly. The greater the force 
which is opposed to it, the more quickly it may be 
brought to rest, but unless its motion is opposed by 
some force, it continues to move indefinitely without 
change of velocity. 

The flow of current from the condenser, then, does 
not cease when the condenser has discharged itself, 
and, as a result, that plate which was originally at 
the lower potential takes on a higher potential than 
the other. The condenser is beginning to charge up 
in the opposite direction. The potential difference of 
the plates now acts in such a direction as to oppose 
the flow of the current, which decreases continually 
as the potential difference of the plates rises. If the 
resistance of the circuit were zero, the current would 
be zero (reversing) at that moment when the po¬ 
tential difference of the plates had become just equal 
to the original value. This is, the condenser would 
be as fully charged as at the beginning, only with 
the potential difference of the plates in the direction 
opposite to that at the start. Now begins a discharge 
of electricity from the condenser in the opposite direc¬ 
tion to the first discharge, and this discharging cur¬ 
rent flows until the condenser has become fully re¬ 
charged in the original direction. The cycle of 
operations then repeats itself, and so on, over and over 
again. 

The action in the circuit may thus be described as 
a flow of electricity around the circuit, first in one 





96 TEXT BOOK ON RADIO 


direction and then in the other. The rate of flow 
(current) is greatest when the plates have no po¬ 
tential difference, and the current becomes zero and 
then begins to build up in the opposite direction at 
the moment when the potential difference of the plates 
reaches its maximum value. This alternate flow of 
electricity around the circuit first in one direction and 
then in the other is known as an “electrical oscilla¬ 
tion.” Since no outside source of emf., such as an 
a.c. generator, is acting in the circuit, the oscillations 
are said to be “free” oscillations. 

Mechanical free oscillations are well known. Such, 
for example, are the swinging of a pendulum and the 
vibration of a spring which has been bent to one side 
and then let go. In the case of the pendulum the 
velocity with which it moves corresponds to the value 
of the current in the electrical case, while the height 
of the pendulum bob corresponds to the potential dif¬ 
ference of the condenser plates. When the bob is at 
its highest point its velocity is zero, corresponding to 
the condenser when the plates are at their maximum 
potential difference and no current is flowing. When 
the pendulum bob is at its lowest position it is moving 
most rapidly. Similarly, when the plates of the con¬ 
denser have zero potential difference, the current flow¬ 
ing has its maximum value. The pendulum does 
not stop moving when it passes through its lowest 
point; neither does the current cease at the moment 
when the condenser plates are at the same potential. 
The pendulum rises with a gradually decreasing 
velocity toward a point at the other end of the swing 
as high as the starting point. The current gradually 
decreases as the condenser charges up to an opposite 
potential difference equal to the original value. The 





DAMPING 97 


return swing of the pendulum corresponds to the 
flow of current in the direction opposite to the original 
discharge. 

A pendulum swinging in a vacuum and free from 
all friction would continue to swing indefinitely, each 
swing carrying it to the same height as the starting 
point. Similarly, electric oscillations would persist 
indefinitely in a circuit—that is, they would be ‘‘un¬ 
damped” if there were no resistance to the current. 

Actually, electric oscillations die down in a circuit 
and finally cease altogether, just as an actual pendu¬ 
lum will make shorter and shorter swings and finally 
come to rest. Since the occurrence of free oscillations 
in a circuit presupposes no interference with the cir¬ 
cuit from outside, the circuit receives no energy 
beyond that imparted to it at the moment when the 
oscillations begin. Thereafter the circuit is self-con¬ 
tained, and any loss of its energy in heat and elec¬ 
tromagnetic waves reduces by just so much the energy 
available for maintaining the oscillations. This loss 
of energy goes on continuously and the oscillations die 
away to nothing. They are said to be “damped” 
oscillations. 

At the start there is a definite amount of energy 
present in a circuit, namely, the energy of the charge 
given the condenser. The amount of this energy de¬ 
pends upon the capacity of the condenser and the 
square of the potential difference between its plates 
(emf. to which it is charged). This energy exists in 
the dielectric of the condenser, which is in a strained 
condition due to the charge. As soon as the current 
begins to flow the condenser gives up some of its 
energy, and this begins to be associated with the cur- 
rent and is to be found in the magnetic field around 

7 







98 


TEXT BOOK ON RADIO 


the current; that is, principally in the region around 
the inductance coil. As the current rises in value 
under the action of the emf. of the condenser, energy 
is continually leaving the condenser and being stored 
in the magnetic field of the inductance coil. When 
the plates of the condenser have no potential differ¬ 
ence, the whole energy of the circuits resides in the 
magnetic field of the coil and none in the condenser. 
Energy is then drawn from the coil as the current de¬ 
creases and energy is stored up in the condenser as it 
is recharged. 

If the resistance of the circuit were zero and no 
energy were radiated in waves or dissipated in other 
ways, the total energy of the circuit would be con¬ 
stant. The energy dissipated in heat and electric 
waves is, however, lost to the circuit, so that the total 
amount of energy, found by adding that present in 
the condenser to that in the inductance, steadily de¬ 
creases. Finally all the original store of energy given 
the circuit has been dissipated and the oscillations 
cease. 

The energy lost when a steady current is flowing in 
a circuit depends not only on the value of the current, 
but on the resistance of the circuit, and in a radio 
circuit this resistance is replaced by a somewhat 
larger quantity of the same kind, the “effective 
resistance.” The greater the effective resistance the 
greater the amount of energy dissipated per second 
when a given current flows. 

Ohm’s law shows that to keep a current I flowing 
through a resistance R an emf. HI is necessary and 
this has to be furnished by the battery, generator, or 
other source. In an oscillating circuit the same is 
true, and that portion of the emf. in the circuit which 










DAMPING 


99 


is employed in forcing the current against the resist¬ 
ance is, of course, not available for charging the con¬ 
denser or building np the discharge current. The 
changes of current in the circuit described above are 
thereby hindered, and the current does not rise to as 
great a value as it would in the absence of resistance. 
The maximum of emf. between the plates of the con¬ 
denser is less each time the condenser is discharged, 
and thus the oscillations of the current die away. 

A good analogy to damped electrical oscillations in 
a circuit is found in the vibrations of a flat spring, 
clamped at one end in a vise, and then bent to one 
side and released. The spring vibrates from side to 
side with decreasing amplitude, until finally it comes 
to rest in its unbent position. When the spring is bent 
energy is stored up in it—the energy of bending. On 
being released the spring moves and gains energy of 
motion, while the energy of bending decreases. If 
there were no friction the loss of one kind of energy 
would be just offset by the gain of the other kind 
and the sum total would remain constant. The spring 
would move past the natural undisturbed position,- 
under the influence of its energy of motion, and would 
be brought to rest at a position just as far to the 
other side as was the starting point. 

Friction has, however, the effect of opposing the 
motion and causing a dissipation of energy in heat, 
and each excursion away from the resting point is 
smaller than the one preceding. 

Free oscillations, then, can take place in a circuit 
containing inductance and capacity. These would 
be undamped in the ideal case where the resistance 
can be regarded as zero. In all practical cases of free 
oscillations, however, the oscillations are damped. To 





100 TEXT BOOK ON RADIO 


produce undamped waves it is necessary to provide 
some source of power to make good the energy dissi¬ 
pated in the oscillating circuit. Strictly speaking, 
undamped free oscillations are impossible in actual 
circuits. It is of importance to study the effect of the 
resistance in determining the rapidity with which the 
oscillations die away. 





WHAT HAPPENS IN A THANSMITTING 

SET 


An alternating current of low voltage enters the 
primary coil of the transformer, and sets up a mag¬ 
netic field around the iron core. The secondary coil 
of the transformer cuts the lines of magnetic force 
and carries a new current of high voltage to the con¬ 




denser. The condenser discharges a current of suf¬ 
ficient high voltage to jump between the terminals of 
the spark gap, and in so doing sets up an interchange 
of electrical energy between the condenser and coil 
No. 1. Fig. 26. This exchange of energy takes place at 
a frequency determined by the size of the coil No. 1 
and the condenser. By regulating the size of coil No. 1 

101 





















102 TEXT BOOK ON RADIO 


and the condenser, the size of the wavelength may 
be regulated as desired. This circuit is termed an 
“oscillating circuit” because the electrical energy 
oscillates between the condenser and the coil. The 
fluctuation of the current in coil No. 1 will induce 
an alternating current in coil No. 2, providing the 
two coils are in close proximity and are properly ad¬ 
justed, and it will carry this current to the trans¬ 
mitting aerial, which will set up the desired disturb¬ 
ance in the ether and start off the electro-magnetic 
waves on their journey. 



Fig. 27—Variable Contact Switch 





THE WESTINGHOUSE TUBE TRANS¬ 
MITTER 


The Type TF Vacuum tube transmitter is designed 
for Radio communication over distances of at least 
fifteen miles by telephone or one hundred miles by 
continuous wave telegraphy. 

Four 5-watt Radiotron U.V. 202 tubes, or equiva¬ 
lent, are used, the four tubes being connected in 
parallel for continuous wave telegraphy. For tele¬ 
phone transmission two of the tubes are used as oscil¬ 
lators and two as modulators. 

A four pole double throw anti-capacity switch is 
provided for throwing from telegraph to telephone. 
The filament of the tubes are heated by a step-down 
transformer, the primary of which is connected to 
the 105 to 115 volt lighting circuit, the primary 
being tapped for 105, 110 or 115 voltage supply. 
This transformer is contained within the set. 

The plate voltage for the tubes should range be¬ 
tween 350 and 500 volts and may be obtained from 
any direct current source. The Westinghouse Electric 
& Manufacturing Company’s 100-watt motor gener¬ 
ator set Style No. 307212 is especially adapted for 
this purpose. The plate voltage source is fed to the 
tubes through audio and radio frequency choke coils. 
A .75 mfd paper condenser is shunted across the 
generator leads. 

The Grid bias voltage for the modulator tubes is 
obtained by connecting a resistance variable in steps 
of 50 ohms, from 50 to 150 ohms, between the nega¬ 
tive generator lead and the filament of the tubes. 

103 


104 TEXT BOOK ON RADIO 


A relay is provided for continuous wave telegraph¬ 
ing, the contacts of which open the negative lead of 
the plate supply, the magnet coil of the relay being 
energized by the 6-volt microphone battery in series 
with the telegraph key. The relay contacts are 
shunted by a condenser of .05 mfd capacity. 

For telephone operation a microphone is connected 
in series with the 6-volt battery and primary of the 
modulation transformer, the secondary of this trans¬ 
former being connected to the modulation tube fila¬ 
ments and grids. 

Coupling between the oscillator tube grids and 
plates is effected through mica condensers and taps 
on the Antenna Loading Inductance. The oscillating 
circuit consists of antenna, radio frequency ammeter, 
loading inductance and counterpoise. 

Binding posts are provided on the panel for con¬ 
necting the telegraph key, 6-volt battery and micro¬ 
phone. The 110-volt A.C. supply to the filament 
transformer is connected by means of flexible cord 
brought out at the left hand end of the set. Binding 
posts are provided within the set for connecting the 
plate voltage supply. 

The loads from the antenna and counterpoise are 
brought into the set through bushed holes in the back 
of the box and connected to binding posts on the 
Antenna Loading Inductance. 

Operation 

Connect the 105, 110 or 115-volt supply to the 
proper posts on the primary of the filament trans¬ 
former. Connect the plate voltage supply to the 
proper binding posts, positive lead of the generator 
to positive binding posts. Connect the antenna and 





TRANSMITTERS 


105 


counterpoise through the bushed holes of the box to 
the binding posts within the set marked antenna and 
counterpoise, connect the 6-volt microphone battery 
to the binding posts on the panel which are so marked. 

Telegraphing 

Throw the transfer switch to the position marked 
“CW” and bring the plate voltage up to 350 volts. 
Close the telegraph key and note radiation, ammeter 
should read 1.7 to 1.9 amperes. Oscillation should 
take place the instant the key is pressed. 

Telephony 

Throw the transfer switch to the position marked 
“Phone” and with 350 volts on the plate the radia¬ 
tion should be 1.2 to 1.4 amperes. When a loud tone 
is sounded into the microphone the antenna current 
should increase .1 to .2 amperes. 

The speech as received on a crystal or a single tube 
detector, in the vicinity of the set, will be found to 
be very clear and understandable and the generator 
and 60 cycle hum will be negligible in volume com¬ 
pared with the speech. 

When a higher voltage than 350 is used on the plate 
a further increase of grid bias within the set will be 
necessary. 

The proper antenna for this set would be one of 
four wires spaced 2]/ 2 ft. and 75 ft. in length. A 
counterpoise having the same dimensions as the an¬ 
tenna and separated from the antenna by 20 to 50 
ft. would give much better results than a ground 
due to its having lower losses. The capacity of the 
above antenna would be approximately .0005 mfd. 












106 TEXT BOOK ON RADIO 



Fig. 28— y >2 K.W. Transmitter 


l 
































TRANSMITTERS 


107 


Apparatus for Undamped Wave Transmission 

Undamped oscillations are not broken up into 
groups like damped oscillations. Exactly similar cur¬ 
rent cycles follow one another continuously, except as 
they are interrupted by the sending key or subjected 
to variations in amplitude. The principal sources of 
undamped oscillations are the high-frequency alter¬ 
nator, the arc converter, and electron tubes. The 
timed spark transmitter emits waves which are only 
very slightly damped. 

For transmission over long distances, as between 
the United States and France, it has been found that 
much better results are usually obtained by the use 
of undamped waves. Damped waves are, however, 
still used for some long-distance work. Desirable 
characteristics in transmitting apparatus for use in 
long-distance work are that it should generate a 
“pure wave’’—that is, a fundamental wave in which 
practically no harmonics are present—that it should 
provide reliable service economically, that it can be 
manufactured in units of large size, that it be adapted 
to high-speed signaling, and that it will efficiently 
generate a wave of considerable length. For long¬ 
distance work it is in fact essential that long wave 
lengths be used. Thus the usual wave length used 
by the Annapolis 500-kw. arc station is about 17,100 
meters, and the usual wave length used by the New 
Brunswick 200-kw. high-frequency alternator station 
is 13,600 meters. 

Principal advantages obtained by the use of un¬ 
damped waves are the following: (1) Radiotelephony 
is made possible if a pure wave can be obtained. 
(2) Extremely sharp tuning is obtained, and it is 







108 TEXT BOOK OX BADIO 


possible for two nearby stations to work on wave 
lengths which are very close together without inter¬ 
fering with each other. The tuning is, in fact, so 
sharp that a slight change of adjustment throws a 
receiving set out of tune and the operator may pass 
over the correct tuning point by too rapid a move¬ 
ment of the adjusting knobs, particularly on the 



Fig. 29—American Badio Transmission Set 


shorter wave lengths. (3) Since the oscillations go 
on continuously instead of only a small fraction of 
the time, as in the case of damped waves, their am¬ 
plitudes need not be so great, and hence the voltages 
applied to the transmitting condenser and antenna 
aie lower. The antenna is often the most expensive 
part of the transmitting station, and since the radiat- 



















TRANSMITTERS 


109 




Hh 

rkXD 


F 






c 




/j5 


/ 

—, 






mu 


V 


J 


J1 


M 




ShuUL 


& 

\ 

2W 

BJlfi/i 



¥ 

\ 



\ 




1 


-dsmsir 


ii' 


§ 


Fig. 30 





































































110 


TEXT BOOK ON RADIO 


ing power of an antenna is limited by the maximum 
voltage during one impulse the radiating power of a 
given antenna is much greater with a generator of 
continuous waves than with a spark transmitter. 

(4) Very sensitive methods of reception can be used, 
particularly beat reception, which increases the range 
to which an undamped wave station can work. 

(5) With damped waves, the pitch or tone of received 
signals depends wholly upon the number of sparks 
per second at the transmitter. When the beat method 
is used for receiving undamped waves the receiving 
operator controls the tone of the received signals, and 
this can be varied and made as high as desired to 
distinguish it from strays and to suit the sensitiveness 
of the ear and the telephone. These advantages— 
freedom from interference from other stations 
through selective tuning, the use of high tones, and 
the greater freedom from strays—combine to permit 
a higher speed of telegraphy than could otherwise be 
obtained. 





WIRE TELEGRAPHY AND TELEPHONY 

An ordinary wire telegraph system consists'simply 
of an electric circuit connecting two stations and 
simple equipment inserted directly in the line at each 
station. The same kind of equipment is generally 
used at each station, and communication can he had 
in either direction. On short lines the equipment of 
each station consists of a “key” and a “sounder” 
connected in series in the line. The key is a simple 
device for rapidly opening and closing the circuit and 
is so constructed that it can be conveniently and 
rapidly operated by hand. There is only a small 
clearance between the contacts of the key. When the 
key is not being operated and is up in its normal posi¬ 
tion the circuit is open. At all times when no signals 
are being transmitted at a given station the terminals 
of the key are short-circuited by a switch. The 
sounder is an electromagnet with an armature so 
mounted, close to the poles of the electromagnet on a 
pivoted arm, that the armature moves through a small 
distance when the current passes through the magnet 
windings. The end of the arm moves between two 
fixed tops, which may be screws. The arm moves in 
accordance with the current impulses on the line, 
corresponding to the opening and closing of the key 
at the distant station, and the contact of the end of 
the arm with the stops causes a click both when con¬ 
tact is made with the lower and with the upper stop. 
Signals are transmitted by means of depressing the 
key to make “dots” and “dashes.” A dot is made 

ill 


112 


TEXT BOOK ON RADIO 


by depressing the key for an instant; a dash is made 
by holding the key down a little longer. A dash is 
equal in length to three dots. Messages are trans¬ 
mitted by a “code” or arrangement of groups of dots 
and dashes representing the letters of the alphabet. 
The code use on land lines in the United States is 
the “Morse” code. On the Continent of Europe land 
lines use the “Continental” code or “International 
Morse code. ’ ’ This code is used throughout the world 
in radio telegraphy. 

In ordinary practice there is only one wire be¬ 
tween two stations, and one terminal of the station 
apparatus at each end is connected to the earth, 
through which the return current flows. Ordinarily a 
number of intermediate stations are cut in on a tele¬ 
graph line at points between the two terminal sta¬ 
tions. Telegraph lines are usually operated as closed 
circuits—that is, current is flowing through the line 
at all times except when the line is actually in use 
for transmitting signals. The power for operation 
may be supplied by a closed-circuit battery, such as a 
battery of ‘ ‘ gravity ’ ’ cells, or by a direct-current gen¬ 
erator. On all except short lines the line current is 
not strong enough to operate a sounder directly so 
that signals can be read, and a relay is connected in 
the line. The operation of the relay by the line cur¬ 
rent opens and closes a local circuit which operates 
the sounder. 

The telegraph system here described represents the 
simplest case. In actual practice many modifications 
may be made. Signals may be transmitted and re¬ 
corded at high speed by automatic apparatus. There 
are very few operators who can copy as many as 50 
words per minute, but with automatic apparatus sev- 







WIRE TELEGRAPHY 


113 


eral hundred words per minute may be transmitted. 
With suitable apparatus it is possible at one time to 
transmit several messages over the same wire without 
one message interfering at all with the others; this is 
called “multiplex” telegraphy. 

In ordinary telephony the voice itself is electrically 
transmitted over wires and reproduced at a distant 
point. The essential parts of a simple telephone sys¬ 
tem are (a) a device called the “transmitter,” by 
means of which sound vibrations cause corresponding 
variations of an electric current, (b) a device for 
changing the electric current variations back into the 
corresponding sounds, and (c) an electric circuit for 
connecting the two devices. 

In the telephone exchanges in use in large cities 
the connecting circuit and switching apparatus are 
very intricate. In some cities automatic switching 
equipment is in use for connecting subscribers at the 
central office. This equipment operates automatically 
directly under the control of the calling subscriber, 
without an operator at the central office, and may he 
very elaborate. 

The device by means of which sound vibrations 
cause corresponding variations of an electric current 
is usually the carbon microphone transmitter. This 
type of transmitter is a speech-controlled variable re¬ 
sistance, and its operation is based on the fact that 
the resistance of carbon varies with pressure changes. 
A low voltage, as from a battery of a few cells, is 
connected to opposite sides of a small cup containing 
carbon granules. The pressure on the carbon granules 
is controlled by the position of a metal diaphragm on 
which the sound is impressed. 

Fig. 31 shows a telephone transmitter of a type 

8 





114 


TEXT BOOK ON RADIO 


which is in general use throughout the United States, 
called the “ solid-back ’ 9 transmitter. This name is 
used because the cup containing the carbon granules 
is supported on a solid back which consists of a 
metal bar attached at its ends to the case of the 
transmitter. In the figure D is the diaphragm, usually 



an aluminum disk about 2 y 2 inches in diameter. T 
is the solid back, on which is mounted the metal cup 
B, containing the carbon granules C. At the back 
of the cup is a small hardened carbon plate E , which 
serves as one electrode of the carbon microphone. At 
the front is another very hard carbon plate F, which 




























































WIRE TELEPHONY 


115 


serves as a lid for the small metal cup. The diameter 
of this plate is a little less than the diameter of the 
inside of the cup, but the cup is completely closed by 
a flexible mica disk, which is attached to the rim of 
the cup and to the carbon disk. This carbon lid or 
cover forms the second electrode of the transmitter. 
The button L attached to the carbon plate F is main¬ 
tained in contact with the diaphragm by a metal 
spring S, which serves also to damp the vibrations 
of the diaphragm. The space between the carbon 
cover F and the back electrode E is nearly filled with 
carbon granules, and the electrodes E and F are so 
insulated that the electric current in the transmitter 
circuit, in passing from one electrode to the other, 
passes through the entire mass of carbon granules. 
The two wires leading to the transmitter are connected 
to the binding posts G and H. The metal face K of 
the transmitter is made heavy to prevent excessive 
vibration, and the exposed metal parts are usually 
insulated from the current-carrying parts. In prac¬ 
tice it is not usually found desirable to have the 
transmitter extremely sensitive, because outside noises 
are then transmitted, and it is therefore difficult to 
understand the speech. The current through the 
usual type of microphone transmitter is about 0.2 
ampere, and the power consumed in the transmitter 
is about 2 watts. 

The microphone transmitters used in radiotelephony 
at the present time do not differ essentially from 
those used in wire telephony, and, in fact, the identi¬ 
cal transmitter usually furnished by operating tele¬ 
phone companies can be used for radiotelephony. 

The device by means of which the variations in the 
electric current reproduce the corresponding sounds 





116 


TEXT BOOK ON RADIO 


is the telephone receiver, which is made in a variety 
of forms. The type of receiver, shown in Fig. 32, 
called the “watchcase” receiver, is often nsed in wire 
telephony, and is almost universally used in both 
radiotelegraphy and radiotelephony. Two w T atch- 
case receivers are commonly used together, connected 
by a metallic “ headband,” constituting a “head set.” 
In Fig. 32, C is a cup which is the case of the re¬ 
ceiver. This cup may be metal or hard rubber or a 
composition. In the bottom of this cup a permanent 
magnet of horseshoe shape is placed; the ends of this 
permanent magnet are shown at HH. To the ends of 
the permanent magnet are attached the bent, soft- 
iron pole pieces NP, SQ. The earpiece E is usually 



hard rubber or a composition and is threaded to the 
cup C. Around each pole piece a coil of fine insulated 
wire is wound, forming the windings MM. These two 
windings are usually connected in series, so that the 
received current passes through both windings. 







































WIRE TELEPHONY 


117 


In some instruments for use with feeble currents 
the wire is very fine and the two coils contain some 
thousands of turns, sometimes as many as 10,000 
turns. In the ordinary standard receiver the num¬ 
ber of turns is, roughly, about 1000. The resist¬ 
ance measured with direct current of a receiver for 
wire telephony may vary considerably, but for the 
standard receiver is usually about 100 ohms. A re¬ 
ceiver designed for the very feeble currents some¬ 
times used in radio communication may have a d. c. 
resistance of 8000 ohms, and seldom has a resistance 
of less than 1000 ohms. The coils of a receiver, par¬ 
ticularly those designed for radio work, have con¬ 
siderable inductance, and at high frequencies the im¬ 
pedance in ohms of the coils of the receiver may be 
many times the resistance of the coils measured with 
direct current. The larger the number of turns used, 
the greater is the magnetic effect in the receiver for a 
current of given strength. 

Above the pole pieces and very close to them is a 
thin, circular, soft-iron disk D, called the dia¬ 
phragm.” The diaphragm of a receiver can be seen 
through the hole in the center of the earpiece. The 
distance between the pole pieces and the diaphragm 
is important in determining the sensitivity of the re¬ 
ceiver ; in standard instruments this distance is about 
0.003 inch. The permanent magnet pulls the dia¬ 
phragm toward the pole pieces a certain distance, 
which depends upon the flexibility of the diaphragm. 
The variations in the current in the receiver windings, 
corresponding to the sound vibrations of the voice 
spoken into the transmitter, produce corresponding 
variations in the magnetic field of the pole pieces, 
and the diaphragm moves in accordance with these 






118 


TEXT BOOK ON BADIO 


variations and reproduces the voice spoken into the 
transmitter. 

It is possible to use a telephone receiver as a trans¬ 
mitter. With a circuit containing only two identical 
sensitive telephone receivers and no battery, the same 
instrument can be used alternately as receiver and 
transmitter by the person at each end of the line, and 
speech thus transmitted. This was, in fact, done in 
the early days of telephony, but the currents so gen¬ 
erated by using the receiver as a transmitter are so 
feeble that other devices are now used for practical 
purposes. 

Words spoken into the transmitter vary the pres¬ 
sure of the carbon granules, and hence the resistance 
between the transmitter terminals and corresponding 
variations in the output current of the transmitter 
are thus produced. The nature of the electric cur¬ 
rent transmitted by the wires leading to the receiving 
station depends upon the auxiliary apparatus used 
with the transmitter. The electric current passing be¬ 
tween the stations is often a feeble alternating cur¬ 
rent having a frequency from perhaps 100 cycles per 
second to 3000 cycles per second, considerably higher 
than the frequencies used for commercial lighting pur¬ 
poses. These frequencies, in fact, correspond to the 
frequencies of the sound waves impressed upon the 
transmitter diaphragm. Thus the note “middle C , 97 
which corresponds to a sound wave having 256 vibra¬ 
tions per second, causes an alternating current having 
a frequency of 256 cycles per second. In the case of 
some kinds of telephone systems the wires may trans¬ 
mit a pulsating direct current of several tenths of an 
ampere, whose pulsations correspond to the impressed 
sound waves. 





WIRE TELEPHONY 119 


Speech transmitted by telephone instruments is not 
entirely natural, because th£ vibrating parts, both 
electrical and mechanical, of the telephone equipment 
used produce distortions during the transmission of 
the sound. In the early days of telephony, when 
the causes of distortion were not well understood, seri¬ 
ous effects of this kind occurred when talking over 
very short distances. At the present time it is possi¬ 
ble to talk from New York to San Francisco by wire. 
This result has been attained only after years of ex¬ 
perience and investigation and the development of in¬ 
struments involving principles only recently discov¬ 
ered. Successful transmission over such long dis¬ 
tances requires many refinements in the design of 
every device used. 

It is possible at the same time to transmit both 
telegraph and telephone messages over the same line; 
such a line is often called a “composite” line. 

With the currents used in ordinary telephony, it 
is possible at the same time to transmit three tele¬ 
phone messages over two pairs of wires by adding at 
each end a “phantom” circuit, which is an additional 
circuit balanced across the two main circuits through 
suitable impedances. The operation of a telephone 
system so that one pair of wires carries more than one 
message is called ‘ ‘ multiplex telephony. ’ ’ Besides the 
use of the phantom circuit, multiplex telephony can 
be attained by the use of alternating currents of the 
high frequencies used in radio communication. 





RADIOTELEPHONY 


Speech is composed of complex vibrations, and a 
graphic record of the sound wave in air which trans¬ 
mits the simplest word shows a very complex wave 
form. The problem of any form of telephony is to 
accurately reproduce electrically at the distant receiv¬ 
ing station the complex sound wave which is spoken 
into the transmitter. The principles of radiotele¬ 
phony are the same as those of radiotelegraphy by 
undamped waves. In radiotelephony the sending 
key used in radiotelegraphy is replaced by apparatus 
which varies the transmitting antenna current in ac¬ 
cordance with the sound waves produced by the voice. 

There are a number of ways in which a graphic 
record can be made of the wave form of the wave in 
air which corresponds to a given sound. A simple 
method is to record the sound on a phonograph record, 
then play the record slowly, and greatly magnify the 
motion of the needle by a lever arrangement which 
traces the wave. The wave forms corresponding to 
many different sounds have been studied. A tuning 
fork may give nearly a pure sine wave, but the wave 
forms corresponding to most sounds are very complex. 

In the transmission of radiotelegraphic signals by 
undamped waves, the pitch of the note in the tele¬ 
phone receivers is determined in part by the apparatus 
at the receiving station—as, for example, in hetero¬ 
dyne or autodyne reception. For transmission of 
sounds of definite pitch, or for transmission of speech, 
the nature of the received signal must depend upon 

120 


RADIO TELEPHONY 


121 






















































































122 


TEXT BOOK ON RADIO 


the nature of the current in the transmitting aerial. 
In spark transmission the note depends upon the 
number of wave trains per second leaving the aerial, 
this being determined by the speed of the rotary gap 
or the frequency used in charging the primary con¬ 
denser. Spark, tone, and radiotelephone transmit¬ 
ters differ from transmitters of undamped waves in 
that the strength of the radio-frequency antenna cur* 
rent is varying at an audio frequency. Ordinarily, 
the radiation from a spark transmitter is treated as 
being composed of successive trains of waves of radio 
frequencies. An alternative method is to describe it as 
a single wave whose amplitude is varying at audio 
frequencies. 

An alternating current is said to be modulated when 
the amplitude of its oscillations is varied periodically. 
The frequency at which the variations occur is neces¬ 
sarily less than the frequency of the alternating cur¬ 
rent which is being modulated. The nature of the 
variations may assume almost any form. Thus we 
may have dot-and-dash modulation, “chopper” modu¬ 
lation, buzzer modulation, sine-wave modulation (as 
at 800 cycles), and speech modulation. Speech modu¬ 
lation of radio-frequency currents radiated through 
space constitutes radiotelephony. Chopper, buzzer, 
and sine-wave modulation are often referred to under 
the general name of “tone modulation.” 

When the usual dot-and-dash code signals are trans¬ 
mitted by undamped radio-frequency waves which 
have not been modulated at the transmitting station 
by a chopper, buzzer, 800-cycle alternating current, 
or similar method, it is necessary to use at the receiv¬ 
ing station a chopper, heterodyne, or similar method. 
The dot-and-dash interruption of the transmitted wave 






RADIO TELEPHONY 


123 





s 



c 

4 - 

Hf-HH 




$ 


Fig. 34. 


Direct Cnrrent C.W. and I.C.W. Circuit 



























































124 TEXT BOOK ON RADIO 


constitutes, however, a variation of the transmitted 
wave, which is a form of modulation, and causes ‘ ‘ side 
waves” having wave lengths irregularly distributed 
over a band. When dot-and-dash signals are trans¬ 
mitted at high speeds by automatic devices the band 
of wave lengths between the side frequencies is 
broader, and greater interference is caused. When 
automatic devices are used for both transmitting and 
receiving, the transmitting station does not usually 
transmit the signals of the International Code, but a 
series of impulses arranged only with regard to the 
most convenient operation of the apparatus. 

When a radio-frequency wave is modulated by an 
audio-frequency wave the amplitude of the resultant 
wave at each instant is determined by the product of 
the instantaneous value of the amplitude of the radio¬ 
frequency wave at that instant. Thus modulating 
action should be carefully distinguished from hetero¬ 
dyne action, since in heterodyne action the instan- • 
taneous value of the resultant is determined by the 
sum of the instantaneous values of the two component 
radio-frequency waves. 

In modulating action the audio-frequency wave 
whose amplitude is multiplied by the amplitude of 
the radio-frequency wave is ordinarily the sum of an 
audio-frequency wave (alternating current) and an 
unvarying component (direct current). The ampli¬ 
tude of the radio frequency is varied periodically 
above and below a certain value which is not zero. 

For rough purposes of illustration of the process 
of modulation, the unmodulated radio-frequency wave 
can be thought of as a plastic substance which is 
molded in a form shaped like the form of the audio¬ 
frequency modulating wave. An illustration of a 






RADIO TELEPHONY 


125 



Fig. 35. Alternating Current Radiophone Circuit 












































































126 TEXT BOOK ON RADIO 


similar process is found in the impression of the 
wave form of a voice on the plastic wax of a master 
phonograph record, from which many records are 
made which will faithfully reproduce the voice. In 
radiotelephony the wave form of the voice, impressed 
on the radio-frequency carrier wave, is reproduced at 
many receiving stations. 

The strength of the received signal depends not 
only on the average radio-frequency amplitude hut 
also on the degree to which it is changed or modu¬ 
lated. An alternating current is said to be com¬ 
pletely modulated when the amplitude of its oscilla¬ 
tions is periodically reduced to zero. 


i 





RADIO TELEPHONY 


127 


«o Va 






iQQQOQQQ 


Vo 1 ’ 




MMMJ 



Fig. 36—Self-rectifying C.W. Telegraph Circuit 

















































VACUUM TUBES 


During the past few years there has been added 
to the apparatus employed in radio communication a 
new device, called the “electron tube/’ which has 
made possible many important advances in the art. 
A small electron tube of a simple type resembles 
closely in general appearance an ordinary 10-watt 
incandescent electric lamp. Since these tubes may 
be used for a variety of purposes—to generate, to 
amplify, and to modulate radio oscillations, as well 
as to detect them—they now are used in most types 
of radio apparatus. New applications have come 
rapidly, and there is every reason to believe that 
further developments may be expected. The electron 
tube is of primary importance in radio communica¬ 
tion, but it has many important applications in other 
fields of electrical engineering, particularly in ordi¬ 
nary telephony with wires, where its use makes possi¬ 
ble conversation between points separated by a dis¬ 
tance of 3000 miles. One fact of importance is that 
such tubes make possible the use of apparatus that is 
easily portable—a primary consideration in military 
communication, and of importance also in various com¬ 
mercial applications. The principles which underlie 
the operation of electron tubes and their action under 
the widely different conditions met in actual practice 
therefore deserve careful study. 

The name “electron tube” is derived from the fact 
that the action of the tube is due to very small par¬ 
ticles of matter called “electrons.” An electron is 


128 


EDISON EFFECT 129 


much smaller than an atom, and is the building block 
of which atoms are constructed. An idea of the ex¬ 
tremely small size of the electron may be obtained 
from the estimate that in a very tiny spherical globule 
of copper having a diameter of one one-hundred-thou¬ 
sandth of an inch, there are about 20 billion electrons. 
The atom was formerly regarded as the smallest par¬ 
ticle of matter which could exist; something like 
25,000 hydrogen atoms would have to be placed in 
contact in a row to make up a length of one ten-thou¬ 
sandth of an inch. The weight of an electron is only 
about one two-thousandths of the weight of a hydro¬ 
gen atom. An electron carries a charge of negative 
electricity whose value can be measured. Since the 
comparatively recent general recognition by scientific 
men of the existence of the electron, many ideas for¬ 
merly held as the explanations of various physical 
phenomena have been considerably modified. The 
fact that the electron carries a charge of negative 
electricity makes possible the use of the electron tube 
in radio communication. 

If two wires are connected to a battery, one to 
each terminal, the other two ends of the wires may 
be brought very close together in air, yet so long as 
they do not touch no current flows between them. The 
two ends may be inclosed in a bulb like that of an 
incandescent electric lamp and the air pumped out, 
and still so long as the ends are separated no current 
will flow. Thus, when the filament in an incandescent 
electric lamp breaks, the current stops and the light 
goes out. 

About 1884 Edison discovered that if inside an ex¬ 
hausted incandescent electric lamp of the ordinary 
type, containing a filament whose two ends were con- 

9 






130 TEXT BOOK ON RADIO 


nected to two wires insulated from each other, there 
was introduced a third wire insulated from the fila¬ 
ment connections and maintained at a voltage positive 
with respect to the filament, then a current would flow 
across the vacuum inside the tube from the third wire 
to the filament as long as the filament was incandes¬ 
cent, but that the current ceased as soon as the fila¬ 
ment became cold. This phenomenon is generally 
called the “Edison effect.” It is due to the fact that 
the incandescent filament shoots off electrons at high 
velocity, each carrying its charge of negative elec¬ 
tricity, and that the electrons are attracted to the 
positively charged third wire. The passage to the 
third wire of the negative charges of the electrons 
is equivalent to the flow of a current between the 
filament and third wire. In order that a current of 
one-billionth of an ampere should flow between the 
filament and the plate, it is necessary that more than 
six billion electrons should pass each second from 
the filament to the plate. It should be particularly 
noted that while the electrons move from the heated 
filament to the cold third wire, the current passes 
from the third wire to the filament, according to the 
usual idea that the direction of an electric current is 
from the positive (higher) to the negative (lower) 
voltage. This distinction between the direction of 
electron flow and the direction of current floiv should 
be carefully noted. 

As each electron leaves the filament, the filament 
acquires a charge of positive electricity equal in 
amount to the negative charge carried by the electron. 
If no voltage is applied to the third wire, electrons 
will still be emitted by the incandescent filament, but 
will travel only a very short distance before being 





VACUUM TUBES 131 


attracted back to the filament by the positive charge 
acquired by the filament. The voltage applied to the 
third wire must be sufficient to overcome this attrac¬ 
tion of the filament. No current will flow if the nega¬ 
tive terminal of the battery is connected to the third 
wire, because the electrons will not be attracted by 
the negatively charged third wire, and, in fact, will 
be repelled back into the filament. 

A tube containing a filament and one additional 
wire or other piece of metal, is called a two-electrode 
tube, the filament being considered as one electrode, 
and the additional piece of metal the scond electrode. 

The above explanation of the mechanism of the 
flow of current between the filament and plate in an 
electron tube applies to a tube having a very perfect 
vacuum. If there is more than the merest trace of 
gas remaining in the tube, the operation is more com¬ 
plicated, and a larger current will usually flow with 
the same applied voltage. This happens in the fol¬ 
lowing manner. 

In a rarefied gas some of the electrons present are 
constituent parts of atoms and some are free. These 
free electrons move about with great velocity, and if 
one of them strikes an atom it may dislodge another 
electron from the atom. Under the action of the emf. 
between plate and filament the newly freed electron 
will acquire velocity in one direction—the direction in 
which the colliding electron is moving—and the posi¬ 
tively charged remainder of the atom, called an 
“ion,” will move in the opposite direction. Thus 
both of the parts of the disrupted atom become car¬ 
riers of electricity and contribute to the flow of cur¬ 
rent through the gas. This action of a colliding elec¬ 
tron upon an atom is called “ionization by collision, 





132 TEXT BOOK ON RADiO 


and, on account of it, relatively large plate currents 
are obtained in electron tubes having a poor vacuum. 
The earlier tubes were of this sort, but at the present 
time most tubes are made with a better vacuum than 
formerly, so that ionization by collision is responsible 
for but a small part of the current flow. 

At first it would seem to be an advantage to have 
ionization by collision, because a larger plate current 
can be obtained, but there are two difficulties which 
have proved so great that tubes are now usually so 
made as to have only the pure electron flow. The 
first of these difficulties is a rapid deterioration of the 
filament when there is flowing a large plate current 
which is caused by ionization by collision. The posi¬ 
tively charged parts of the atoms are driven violently 
against the negatively charged filament, and since 
they are much more massive than electrons (an 
oxygen or nitrogen ion has about 25,000 times the 
mass of an electron), this bombardment actually seems 
to tear away the surface of the filament. A second 
disadvantage of tubes with poor vacuum is that too 
large a battery voltage may cause a “blue-glow” dis¬ 
charge. 

Two similar tubes with poor vacuum seldom, if ever, 
contain just the same quantity of gas, and therefore 
their electrical characteristics may be considerably 
different. For this reason it is not ordinarily prac¬ 
ticable to connect in parallel two tubes having poor 
vacuum. Tubes with high vacuum, on the other hand, 
can be constructed very uniformly, so that a number 
can be connected in parallel. It is often advantage¬ 
ous to be- able to connect several tubes in parallel in 
generating sets. 

Tubes containing a little gas, i. e., having a poor 





SOFT TUBES 133 


vacuum, are often called ‘ ‘ gas tubes, ’ ’ or ‘ ‘ soft tubes. ’ ’ 
Tubes with high vacuum are often called “hard 
tubes/’ “Soft” tubes are particularly useful as de¬ 
tectors, and if properly selected and used may be 
much more satisfactory as detectors than “hard” 
tubes of similar construction. 

Let us consider what happens in a two-electrode 
tube having a good vacuum, when there is a variation 
in either the temperature of the filament or the volt¬ 
age of the battery connected between the plate and 
filament. 

Suppose first that the filament temperature is kept 
constant. Then a definite number of electrons will 
be sent out per second. The number of electrons that 
travel across the tube and reach the plate per second 
determines the magnitude of the current through the 
plate circuit. The number of electrons that reaches 
the plate increases with an increase of the battery 
connected between the plate and filament (Fig. 
37). If this voltage is continuously increased, a 
value will be reached at which all the electrons sent 
out from the filament arrive at the plate. No further 
increase of current is possible by increasing the volt¬ 
age, and this value of current is called the saturation 
current. 

If now the temperature of the filament is raised to 
a higher constant value by means of the filament¬ 
heating battery and the same voltage steps again ap¬ 
plied, the plate current curve will coincide with that 
obtained before, until the bend is reached; 
then it will rise higher. The explanation of 
this is that the number of electrons sent out by 
the filament increases with the temperatuie ap¬ 
proximately as the square of the excess of the fila- 






134 TEXT BOOK ON EADIO 


ment temperature above red heat, and thus more 
electrons are available to be drawn over to the plate. 
Thus a higher value of plate current will be obtained 
before reaching the limiting condition when all the 
electrons emitted arrive at the plate. When this 
finally happens, the curve, as before, bends over until 
nearly horizontal. 

Suppose now that the voltage of the plate battery 
is kept at a constant value and the filament tempera¬ 
ture is gradually raised by increasing the current 



A—Battery for Heating Filament. 

B—Battery for Sending Current Through 
Space Between Plate and Filament. 


















VACUUM TUBES 135 


from the filament-heating battery. The number of 
electrons sent out will continue to increase as the 
temperature rises. The electric field intensity due to 
the presence of the negative electrons in the space 
between filament and plate may at last equal and neu¬ 
tralize that due to the positive potential of the plate, 
so that there is no force acting on the electrons near 
the filament. This effect of the electrons in the space 
is called the “space charge effect.” It must not be 
supposed that the space charge effect is caused by 
the same electrons all the time. Electrons near the 
plate are constantly entering it, but new electrons 
emitted by the filament are entering the space, so 
that the total number between filament and plate re¬ 
mains constant at a given temperature. After the 
temperature of the filament has reached a point where 
the effect of the electrons present in the space be¬ 
tween filament and plate neutralizes the effect of the 
plate voltage, any further increase of the filament 
temperature is unable to cause an increase of the cur¬ 
rent. The tendency of the filament to emit more 
electrons per second, because of the increased tempera¬ 
ture, is offset by the increase in space charge effect 
which would result if electrons were emitted more 
rapidly, or, more exactly, for any extra electrons 
emitted, an equal number of those in the space aie 
repelled back into the filament. 

Between the filament and plate of a tube we may in¬ 
sert another piece of metal. This third electrode in¬ 
terposed in the stream of electrons between filament 
and grid is usually in the form of a metallic gauze or 
a grid of fine wires, and is generally called the 
< ‘ grid. ’ ’ A tube which contains a filament, plate, and 
grid is called a three-electrode tube and is capable of 





136 TEXT BOOK ON RADIO 


many more uses than the two-electrode tube. The 
addition of the third electrode makes it possible to 
increase or decrease the current between plate and 
filament through wide limits. If a voltage is im¬ 
pressed upon the grid by means of a third battery 
connected between the filament and grid, the space 
charge effect will be modified. The electrons travel¬ 
ing from filament to plate pass between the wires 
forming the grid. If the grid is given a potential 
which is negative with respect to the filament the 
grid will repel the electrons, but many of them will 
still pass through, and reach the plate, because of 
their high velocity, because the positive plate potential 
still affects them to some extent. If the grid potential 
is made still more negative the plate current will 
diminish until finally it may be stopped entirely. 

Suppose, however, that the grid is given a positive 
potential instead of negative. Electrons are now at¬ 
tracted to the grid as well as to the plate, and more 
electrons are now drawn toward the plate than would 
otherwise pass, so that the plate current increases. 
The charge of the grid partially neutralizes the effect 
of the space charge. As in the two-electrode tube, a 
limit to the magnitude of the plate current will finally 
be reached, when the space charge caused by the large 
number of negative electrons in the tube fully counter¬ 
acts the influence of the positive charges on grid and 
plate. The attainment of the limiting or saturation 
value of the plate current is assisted by the absorption 
of more electrons into the grid if its positive potential 
is increased. This absorption gives rise to a relatively 
small current in the circuit FGCF, which is called 
the grid current. The total electron flow is the sum 
of the nlate current and the grid current. As the po- 












CARE OP TUBES 


137 


tential of the grid is made more and more positive, 
more and more electrons will be absorbed by the grid. 

When using the larger power tubes with transmis¬ 
sion sets certain precautions are necessary to lengthen 
the life of the tube. Most of the damage to tubes 
is caused during the testing and adjustment of the 
circuit, and great care should be taken during these 
periods. 

The life of radiotron tubes can be materially length¬ 
ened by mounting them in the proper position. Radio¬ 
tron No. 13248, Type UV-202 and No. 13247, Type 
UV-203, should be installed in a vertical position, 
while radiotron No. 13246, Type UV-204, may be op¬ 
erated in either a vertical or horizontal position. 
When mounted in a horizontal position the plates 
should be in a vertical plane, with the seal-off tip 
down. On any tube or group of tubes delivering 
over 50 watts A.C. or operated at a plate potential 
above 2,000 volts, a safety spark gap should be pro¬ 
vided between the grid and filament terminals at or 
near the tube socket or mounting. This gap should 
be adjusted to between 1-32 inch and % inch, depend¬ 
ing upon the plate voltage employed and the number 
of tubes and type of tubes used. The life of the fila¬ 
ment of radiotron power tubes is dependent upon its 
temperature, a 3% increase in filament current will 
halve the life of your tubes, and a 5% decrease will 
double the life. Do not use a greater voltage on 
the filament than that specified, and do not overload 
the plate by using an excessive plate voltage. Power 
tube filaments should be burned at constant voltage 

rather than constant current. 

Occasionally in the parallel operation of radiotron 
power tubes ultra high frequency oscillations develop 





138 TEXT BOOK ON RADIO 


in the plate and grid circuits which prevent the real¬ 
ization of full output, and cause excessive plate and 
grid currents. This effect may be avoided by inserting 
an inductance of a few micro-henries (10 turns in 
one layer on a tube 1 inch in diameter is suggested) 
in one or more of the individual grid leads of each 
tube as close to the grid terminal of the socket as 
possible. 

This protective gap should be placed between the 
coil and the grid terminal of the socket. The best 
arrangement is to mount the gap directly on the 
socket terminals and one terminal of the coil directly 
to the grid terminal of the socket. 



Fig. 38—Diagram of Vacuum Tube 















THE ELECTRON TUBE AS A 
DETECTOR 


There are two methods of using an electron tube as 
a detector. 

In the first method the detector tube is connected 
directly across the condenser in the receiving circuit 
(Fig. 40). Suppose the receiving antenna picks up a 
signal. Then oscillations in the tuned circuit LC are 
set up and the radio-frequency alternating voltage 
across the condenser Cl is impressed between the grid 
and filament, bringing about changes in the plate cur¬ 
rent. If the plate current is normally at a point on 
the bend of the characteristic curve the increase of 
plate current when the grid voltage is positive is 
greater than the decrease of plate current when the 
grid voltage is negative. Thus, on the average, the 
plate current is increased while the oscillations due to 
the signal last. In Fig. 39 are shown, roughly, the 
form of (1) the high-frequency oscillations impressed 
upon the grid, (2) the high-frequency variations in 
plate current, (3) the audio-frequency fluctuations of 
telephone current. The frequency with which these 
telephone fluctuations occur in the frequency of the 
incoming wave trains and in order to be heard must 
be within the range of audible sound. The radio¬ 
frequency fluctuations which occur in the plate cur¬ 
rent shown in (2) do not pass through the windings 
of the telephone receivers, because the inductance of 
the coils in the telephone receiver is so great that the 
radio-frequency variations in the plate current cannot 

139 


140 TEXT BOOK ON RADIO 


flow through them, but flow through the capacity ex¬ 
isting between the leads and windings and across the 
by-pass condenser. Thus these radio-frequency varia¬ 
tions are by-passed by this effective capacity of the 



Fig. 39.—Action of Electron Tube as Detector 


leads of the telephone receiver and only the average 
current flows through the inductance of the tele¬ 
phone receiver windings (3). When using this 
method of detection, no current flows in the grid 
circuit because the average value of the grid voltage 
is maintained negative with respect to the filament in 
order to operate on the curved portion of the curve 
showing the relation between plate current and grid 
voltage. 



















TUBE AS DETECTOR 141 


With simple detector action of the kind here de¬ 
scribed, when signals of ordinary intensity are being 
received, the mean value of the change of the plate 
current, for a given operating point on the grid volt¬ 
age-plate current curve, is very nearly proportional 
to the square of the amplitude of the voltage oscilla- 



Fig. 40—Connections for Using Tube as a Detector 

tions impressed on the grid. For very strong signals, 
however, this relation does not hold. This is a relation 
which holds for any detector which operates by virtue 
of the curvature of the curve showing the current 
which it delivers for various impressed voltages. 























142 


TEXT BOOK ON RADIO 


In some cases it is necessary to use an additional 
battery, called a “C” battery, between points / and g 
(Fig. 40) in order to bring the plate current to the 
bend of the characteristic curve. This, however, does 
not change the action; the variations of the plate 
current are brought about by the alternating emf. 
between the terminals of the coil L just as when the 
battery C is absent. It is interesting to note here 
that we are employing resonance in the circuit LC X 
to obtain as large an emf. as possible between the 
terminals of the coil and condenser with a given 
signal. 

If the grid battery voltage is adjusted so that the 
plate current has a value near the upper bend of 
the curve showing plate current plotted against grid 
voltage, instead of near the lower bend, the action 
will be essentially the same, but the effect of the ar¬ 
rival of a wave train will be to decrease momentarily 
the plate current instead of to increase it. As be¬ 
fore, there will be fluctuations of the plate current 
keeping time with the arrival of wave trains, and 
there will be a sound in the telephone of a pitch 
corresponding to the number of wave trains per 
second. 

Care must be taken in the use of receiving tubes 
that the plate battery voltage is never high enough 
to cause the visible “blue glow.” The tube becomes 
very erratic in behavior when in this condition and 
is very uncertain and is not sensitive as a receiver. 
This is because the plate current becomes so large 
that it is unaffected by variations of the grid voltage. 
Characteristic curves will not repeat themselves if the 
tube shows the blue glow, and sharp breaks may ap¬ 
pear in any or all of the curves. Furthermore, the 








TUBE AS DETECTOR 143 


electrodes are heated and may be damaged by the 
blue-glow discharge. 

With many tubes louder signals are obtained if 
the grid is made positive with respect to the nega¬ 
tive end of the filament, so that current flows in the 
grid circuit. Instead of operating on the curved por¬ 
tion of the grid-voltage, plate-current curve the tube 
operates upon the curved portion of the grid-voltage, 
grid-current curve and the straight portion of the 



Fig. 41 


grid-voltage, plate-current curve. When using the 
curvature of the grid-current characteristic in this 
fashion, a condenser is connected in a series with the 
detector tube and with the receiving circuit from 
which the signal voltage is obtained. Now suppose 
that a series of wave trains falls upon the antenna 
of Fig. 41, as shown in (1) of Fig. 42. If the cir¬ 
cuit LC is tuned to the same wave length as the an¬ 
tenna circuit, oscillations will be set up in it and simi¬ 
lar voltage oscillations will be communicated to the 



























144 TEXT BOOK ON RADIO 



Fig. 42 

































































































TUBE AS DETECTOR 145 


grid by means of the condenser C. As shown in (2) 
Fig 42, each time the grid becomes positive the elec¬ 
tron current which flows at the voltage eo will be in¬ 
creased more than it is decreased when the grid volt¬ 
age goes below eo. Thus during each wave train the 
grid will continue gaining negative charge and its 
voltage will, on the average, be mostly negative, as 
shown in (3), Fig. 42. This negative charge on the 
grid opposes the flow of electrons from filament to 
plate and produces a much magnified decrease in the 
plate current throughout the train of oscillations, as 
shown in (4), Fig. 42. At the end of each wave train 
this charge leaks off either through the condenser or 
through the walls of the tube, or both, and the plate 
current becomes steady again at its normal value (4), 
Fig. 42. This should happen before the next wave 
train comes along, and in order to insure this a re¬ 
sistance of about a megohm (a million ohms) is 
shunted across the condenser. Such a resistance is 
called a “grid leak.” As has been stated above, the 
inductance of the coils in the telephone receivers is 
so great that the radio-frequency variations in the 
plate current can not flow through them, but flow 
through the capacity existing between the leads and 
windings and across the by-pass condenser. The cur¬ 
rent which actually flows through the windings and 
operates the telephone receivers, if drawn, will look 
something like the dotted line in (4) and the heavy 
line in (5). Thus, as in the case of the circuit of 
Fig. 40, the note head in the telephone corresponds 
in pitch to the frequency of the wave trains. If the 
waves falling upon the antenna are undamped waves, 
they may be detected using either of these circuits if 
they are first divided off into audio-frequency groups. 

10 





146 


TEXT BOOK ON RADIO 


To receive undamped waves which are not divided into 
groups of audible frequency, electron tubes may be 
used in special ways called the het 2 rodyne and auto¬ 
dyne methods, through tlie high leak resistance, this 
fixes the steady voltage of the grid at about 0.5 to 0.8 
volts positive with respect to the negative end of 
the filament. 

In order to get a readable signal from a good tube 
detector, it is usually necessary to apply to the grid 
a voltage of two millivolts effective value, which would 
correspond approximately to an alternating current of 
about 0.01 microampere in the grid circuit. These 
values apply to a completely modulated wave—that 
is, a wave whose oscillations reach a zero value at 
regular intervals which correspond to the audio fre¬ 
quency of the wave trains. 

The Tube as an Amplifier 

An electron tube acts as a detector or rectifier be¬ 
cause an alternating voltage applied to the grid cir¬ 
cuit can be made to produce unsymmetrical oscilla¬ 
tions in the plate circuit. While the tube is thus act¬ 
ing as a detector it is also, as a matter of fact, acting 
as an amplifier—that is, oscillations of greater power 
are produced in the plate circuit for a given alternat¬ 
ing voltage in the grid circuit than would be produced 
by the same voltage directly in the plate circuit. This 
explains why the electron tube may be a more sensi¬ 
tive detector than the crystal detector, which acts as 
a rectifier only. 

It is sometimes desired to amplify an alternating 
current without any rectifying or detecting action. 
This is done by keeping a voltage on the grid of such 
value that the symmetry of the oscillations in the plate 





TUBE AS AMPLIFIER 147 


circuit is not altered. Thus, if there is a steady volt¬ 
age applied on the grid of such value that the plate 
current is on the part of the characteristic curve that 
is nearly straight, then a small change in grid volt¬ 
age in either direction causes the plate current to 



CiRlQ VourACiB. 

Fig. 43 

increase or decrease the same amount. For instance, 
if the grid voltage is increased from v to w (Fig. 43) 
or decreased by an equal amount from v to u, the 
current will, in the first case, increase from a to c 
and in the second case fall off by an equal amount, 
from a to ~b. In other words, the wave form of the 
grid voltage variation will be repeated in the fluctuat¬ 
ing plate current. The latter will now be equivalent 










148 TEXT BOOK ON EADIO 


to an alternating current superimposed upon the 
steady plate current from the plate battery. The 
magnitude of the alternating-current part of the plate 
current will be greater, the steeper the slope of the 
curve at the point P. 

For the same voltage acting in the two circuits the 
power expended in maintaining the oscillations of the 
grid current is far less than that involved in the cor- 



VOL<AiC t 6>. 


Fig. 44—Effect of Applying Signal to Electron 
Tube Detector 

responding variations in the plate current. The sig¬ 
nals may be thought of as exerting a sort of relay 
action on the plate circuit, causing magnified power 







TUBE AS AMPLIFIER 149 


to be drawn from the plate battery. The tube is said 
in this case to act as an “amplifier.” The variations 
of current in the grid circuit have been compared to 
the slide valve of an engine, since they admit energy 
from the battery into the plate circuit much as the 
slide valve admits energy into the cylinder of the 
engine. The oscillations impressed on the grid circuit 
may be of high radio frequency or of an audible fre¬ 
quency of perhaps 300 to 3000 cycles per second. 




Fig. 45—Action of Rectifier on Received Wave Trains 


To utilize the amplified alternating current in the 
plate circuit, the primary of a transformer T (Fig. 
46) may be placed in the plate circuit. From the 
secondary of this transformer the alternating current 
is delivered to a detector, which may be an electron 
tube operating as a rectifier or a crystal detector. If 
further amplification is desirable, the alternating cur- 











150 TEXT BOOK ON EADIO 


rent from the secondary of the transformer may be 
delivered to the grid circuit of a second amplifying 
tube, as shown in Fig. 46. From the second tube it 
then goes to a detector tube or to a crystal detector. 
This method of successively using two or more tubes 
for amplification is called cascade amplification. The 
last tube in such an amplifier of radio-frequency waves 
is called the detector tube, and the other tubes are 
called amplifier tubes. An amplifier consisting of one 
detector tube and two amplifier tubes is said to have 
two stages of amplification. 

Instead of transferring the amplified energy by 
means of a transformer coupling, the coupling may 



Fig. 46—Cascade Amplification Transformer Coupling 

Connections 


be simply a resistance, or may be a condenser. A 
circuit using resistance coupling is shown in Fig. 47, 
in which the radio-frequency power is amplified by 
two tubes coupled together through resistances, and 
then detected. After passing through the detector, 
the currents of audio-frequency can be further am¬ 
plified by one or more audio-frequency stages. An am¬ 
plifier in which the signal is amplified before reach- 


































TUBE AS AMPLIFIER 151 


ing the detector is called a radio-frequency amplifier. 
An amplifier in which the signal is amplified after 
passing through the detector is called an audio-fre¬ 
quency amplifier. Resistance couplings in radio-fre¬ 
quency amplifiers have been extensively used in 
France, but not to so great an extent in the United 
States. The advantage of a resistance-coupled ampli¬ 
fier is that while the amplification per tube may not 
be so great as with transformer couplings, the amount 
of amplification is practically independent of the 






To 

Detector 

and 

Telephoned 


Fig. 47—Resistance Coupled Amplifier 

wave length for long wave lengths. Resistance- 
coupled amplifiers seldom give full amplification at 
wave lengths below 1,000 meters. In order to get the 
greatest power output, and hence the greatest power 
amplification, from a tube, a resistance should be used 
in the plate circuit of a value equal to the average 
internal resistance of the tube between plate and fila¬ 
ment. In this respect the tube is similar to any other 
electrical machine and to a battery. Usually, how¬ 
ever, such small currents flow into the detector used 
with radio-frequency amplifier that the detector may 
be considered a voltage-operated device, in which case 
the maximum voltage output and not the maximum 






















152 


TEXT BOOK ON RADIO 


power output is desired from the amplifier tubes. 
This is realized by making the coupling resistances 
larger than the internal resistance of the tube be¬ 
tween plate and filament, in some cases two or three 
times as large. These high resistances require higher 
plate voltages than are required for transformer coup¬ 
ling, perhaps voltages two or three times as great as 
for transformer coupling. In some cases, as in some 
military applications, this may be a real disadvantage. 

For audio-frequency amplification, iron core trans¬ 
formers are used. For transformer-coupled radio¬ 
frequency amplification the small transformers used 
generally have air cores—that is, no iron is used. 
There have recently been developed radio-frequency 
transformers with iron cores, very thin laminations 
being used. 

Elementary Theory of Amplification .—The char¬ 
acteristic curves of an electron tube show that an in¬ 
crease in the grid voltage makes a much greater in¬ 
crease in the plate current than the same increase in 
the plate voltage itself would do. A volt added to the 
grid voltage makes eight times as much change in 
the plate current as a volt added to the plate voltage 
would make. This number, which represents the rela¬ 
tive effects of grid voltage and plate voltage upon 
plate current, is called the “amplification coefficient” 
of the tube. The greater the value of this amplifica¬ 
tion co-efficient is for a given value of internal plate- 
circuit resistance of the tube, the more efficient is the 
tube as an amplifier of weak signals. The amplifica¬ 
tion coefficient may be defined at the ratio of the 
change in plate current per volt change on the grid, 
to the change in plate current per volt change on the 
plate. 







THEORY OF AMPLIFICATION 153 


The two principal constants of a tube are the am¬ 
plification coefficient just defined and the internal out¬ 
put resistance or internal plate-circuit resistance. 
The internal plate-circuit resistance is the resistance 
to small alternating currents which exists between 
the plate and the filament in the tube, and, since it is 
the resistance of the output circuit of the tube, is often 
called the internal output resistance. These two con¬ 
stants may be calculated from the characteristic curves 
of the tube or may be measured by a simple method 
like a bridge measurement or may be calculated ap¬ 
proximately from the structural dimensions of the 
tube. The voltage amplification given by an ampli¬ 
fying circuit may be calculated from these two con¬ 
stants of the electron tube. 

The voltage amplification may be defined as the 
ratio of the voltage change produced in the output 
apparatus in the plate circuit to the change in the 
voltage impressed on the grid. Thus, in the resist¬ 
ance-coupled amplifier of Fig. 47, it is the ratio of 
the voltage between a and b at the terminals of R to 
the voltage applied between a and b. Calling the 
amplification coefficient K and the internal output re¬ 
sistance Ro, it can be shown that the voltage amplifica¬ 
tion for such a combination is 

KR 


R -f- Ro 

Audio-Frequency Amplification .—In the preceding 
discussion of amplification it was pointed out that 
after a radio-frequency current is amplified it is 
passed through a rectifying device, often a detector 
tube, and the term “audio-frequency amplifier” was 






154 TEXT BOOK ON RADIO 


defined. If an audio-frequency current is to be am¬ 
plified, it is not necessary to pass the amplified current 
through a detector, since the amplified current is 
audible if received with a telephone receiver placed 
in the plate circuit of the amplifier. It is sometimes 
desired to amplify the audio-frequency current pro¬ 
duced in a radio rectifying device, in which case the 
amplifier is an audio-frequency amplifier. In this 
case the radio current consisting of groups of radio¬ 
frequency oscillations is first impressed upon the de¬ 
tector and the pulses of current having the group 
frequency are passed on into the amplifier. The am¬ 
plifying process may be carried on through several 
steps, as in the cascade amplification shown in Fig. 
46. An amplifier consisting of two Type VT-1 tubes 
in cascade may give a power amplification of 20,000 
times. 

In some amplifiers as many as six tubes may be 
used. In such cases it is general practice to use per¬ 
haps three tubes as radio-frequency amplifiers, then 
the detector tube, and then perhaps two tubes as 
audio-frequency amplifiers. One reason for using the 
radio-frequency amplification is because under proper 
operating conditions with signals of moderate intens¬ 
ity the output of a detector tube is approximately 
proportional to the square of the input voltage, and 
hence the output of the detector tube increases rapidly 
as the input voltage is increased. If more than three 
stages of radio-frequency amplification are used, trou¬ 
blesome regenerative effects are very likely to occur 
in the output circuit of the amplifier. Regenerative 
effects are also likely to occur if more than two stages 
of audio-frequency amplification are used, causing 
“howling” ntfises in the output circuit. If, therefore, 





AUDIO FREQUENCY AMPLIFICATION 


155 


we wish to use as many as six tubes in an amplifier, 
it is necessary to use both radio-frequency and audio¬ 
frequency amplification. These troublesome effects 
can be reduced by properly shielding the various cir¬ 
cuits of the amplifier, as by inclosing in metal. If 
very feeble incoming oscillations are impressed on the 
input of such a six-tube amplifier of a type now in 
extensive use, the over-all voltage amplification of the 
amplifier may be several million. It is only by the 


f 

B 


Fig. 48—Regenerative Circuit for Simultaneous Amplifying 

and Rectifying 


L 



use of amplifiers of this type that it has been possible 
to use the coil antennas, which may be 4 feet square 
or even smaller, as receiving devices and as radio 
compasses. 

Amplifiers with a large number of tubes have been 
used, especially for very short waves, such as 50 
meters. The use of even six tubes requires very care¬ 
ful design to prevent difficulties due to regenerative 
effects. With a greater number of tubes and greater 




















156 TEXT BOOK ON BADIO 


amplification every disturbance is magnified, and even 
greater care in design is essential and shielding is par¬ 
ticularly important. The use of more than six tubes 
in a compact, portable, unit, is especially difficult. A 
six-tube amplifier, properly designed, will usually give 
all the amplification necessary for ordinary purposes. 

The use of radio-frequency amplification for short 
wave lengths, particularly for less than 300 meters, 
is attended with many difficulties caused by the low- 
impedance paths which the capacities between the 
leads and between the elements of the tubes offer at 
high frequencies. For short waves the high frequency 
may be changed before amplification by the beat 
method. 

If an amplifier with transformer coupling or capaci¬ 
tive coupling is to be used on one particular wave 
length a much more effective amplifier can be designed 
than if it is required that the amplifier operate over a 
considerable range of wave lengths. The performance 
of a resistance-coupled amplifier, however, when used 
on long wave lengths depends very little on the wave 
length. Resistance-coupled amplifiers seldom give 
full amplification at wave lengths below 1000 meters. 

The grid of a tube may be maintained at a definite 
voltage above the negative terminal of the filament, 
so that the tube operates at a particular point on 
the characteristic curve showing the relation between 
grid voltage and plate current. For a detector it is 
desirable to have the operating point at the sharpest 
bend in the characteristic curve, as has been explained 
above. For an audio-frequency amplifier it is usually 
desirable to have the operating point at about the 
center of the steepest part of the characteristic curve. 
The d. c. voltage so used is often called a “biasing 





AMPLIFICATION 


157 


potential.” A method of obtaining this biasing po¬ 
tential, which is extensively employed, is by the use 
of a voltage divider arrangement, which consists of 
a resistance of perhaps 200 or 300 ohms connected 
across the filament battery terminals and an adjust¬ 
able contact, which is connected to the grid. 

Stabilizer .—In receiving damped waves or inter¬ 
rupted continuous waves with an amplifier it is neces¬ 
sary to prevent the various tubes in the amplifier from 
oscillating. This may be done by applying a positive 
voltage of the proper magnitude to the grid. The volt¬ 
age divider arrangement just mentioned may be used 
for this purpose, and when so applied to amplifier 
tubes is called a ‘ ‘ stabilizer. ’ ’ The stabilizer is usually 
so adjusted that the circuit of the tube for which it 
is used is just below the oscillating condition. In an 
amplifier of several stages, such as the six-tube am¬ 
plifier mentioned above, having both radio-frequency 
stages and audio-frequency stages, it is desirable to 
have one separate stabilizer for the radio-frequency 
stages and one stabilizer for the audio-frequency 
stages. A separate voltage divider should also be 
used for adjusting the grid potential of the detector 
tube. The use of the stabilizer makes the grid suf¬ 
ficiently positive so that the grid circuit will absorb 
an appreciable amount of power. Stabilizers may be 
used with amplifiers having either inductive, capaci¬ 
tive, or resistance coupling. Stabilizers may greatly 
increase the sensitivity and usefulness of an ampli¬ 
fier and are now found on many radio-frequency am¬ 
plifiers of recent design. , 

Regenerative Amplification .—The sensitiveness of 
an electron tube as a detector may be enormously in¬ 
creased by a method which multiplies its amplify mg 





158 TEXT BOOK ON BADIO 


action. The connections are shown in Fig. 48. The 
explanation of the amplifying action is as follows: 
Oscillations in the circuit LL2C applied to the grid 
through the condenser C-l produce corresponding 



lb 


Fig. 49—Combination Badio and Audio Frequency 

Amplification 

variations in the continuous plate current, the energy 
of which is supplied by the plate battery B, (Fig. 
48.) This plate current flows through L-3, and by 
means of the mutual inductance M some of the energy 
of the plate oscillations is transferred back to the grid 




























REGENERATIVE AMPLIFICATION 


159 


circuit, and the current in the circuit LL2C is thus in¬ 
creased. This produces amplified grid oscillations 
•which by means of the grid, produce larger variations 
in the plate current, thus still further reinforcing the 
oscillations of the system. Simultaneously with this 









50—Combination of Electron Tube Amplifier and 
Crystal Detector 



























160 


TEXT BOOK ON RADIO 


amplification the regular detecting action goes on; the 
condenser C-l is charged in the usual way, but accu¬ 
mulates a charge which is proportional not to the 
original signal strength but to the final amplitude of 
the oscillations in the grid circuit. The result is a 
current in the telephone much greater than would 
have been obtained from the original oscillations in 
the circuit. 

To obtain maximum voltage on the grid, the circuit 
LL2C should have large inductance and small ca¬ 
pacity. The connections between L-2 and L-3 must 
be so made that their mutual inductance is of proper 
sign to produce an emf, which will aid the oscillations 
instead of opposing them. Various modifications of 
this method are used. The condenser C may be across 
L-3, so that the tuned oscillatory circuit is in series 
with the plate instead of the grid; or C may be con¬ 
nected across all of the inductance in series, the oscil¬ 
lation circuit then including L, L-2, and L-3. 

Combination Radio and Audio Regenerative Ampli¬ 
fication .—A single electron tube can be used to am¬ 
plify and detect radio-frequency current and simul¬ 
taneously to amplify the telephone pulses of audio¬ 
frequency. The circuits are shown in Fig. 49. Here 
M 2 represents the coupling for the radio frequency 
and the coils are of relatively small inductance. M 3 
is the coupling for the audio-frequency, and the 
transformer is made up of coils having an inductance 
of a henry or more. The variable condensers C 3 and 
C 4 have the double purpose of tuning M 3 to the audio¬ 
frequency and of by-passing the radio frequencies. 
The radio-frequency variations in the plate current 
flow through the circuit PFL 3 C 4 C 5 L 4 and at the same 
time the audio-frequency variations flow through the 








AUDIO AND EADIO AMPLIFICATION 161 


circuit PFL 3 L C TBL 4 . The audibility of weak signals 
received by this method is about 100 times the audi¬ 
bility obtained with a single tube connected in a 
simple detector circuit. On stronger signals the am¬ 
plification is smaller. 

Electron Tube Amplifier with Crystal Detector .— 
The characteristic curves of an electron tube show that 
the best value of grid voltage for amplification is not 
the same as for best detecting action, which is an argu¬ 
ment for using separate tubes for these two purposes. 
This adds somewhat to the complexity of the ap¬ 
paratus, and in apparatus in which for some reason 
it is desired to use only one tube the combination of 
an electron tube for amplifying and a crystal detector 
for detecting may be used. Such a circuit is shown 
in Fig. 50. 

This oscillating circuit LC is coupled to the antenna 
and is tuned to the frequency of the latter, which is 
the frequency of the incoming waves. The alterna¬ 
tions of voltage between the terminals of the coil L 
are applied between the filament F and the grid G 
through the battery b, which has been previously ad¬ 
justed in voltage so that the plate current has a value 
corresponding to a point on the straight part of its 
characteristic. 

The amplified oscillations in the plate circuit are 
communicated to the oscillating circuit L-l, C-l, which 
is coupled to the plate circuit through the coil M. The 
circuit L-l, C-l, is tuned to the frequency of the re¬ 
ceived waves like the other two circuits. The alterna¬ 
tions of voltage between the terminals of the coil L-l 
are rectified in the crystal detector D in the usual way 
and cause an audio-frequency current to flow through 
the telephone receivers, 
u 





THE ELECTRON TUBE AS A 
GENERATOR 


Conditions for Oscillation .—The electron tube can 
be made to generate high-frequency currents and thus 
act as a source of radio current for the transmission 
of signals and other purposes. Any regenerative cir¬ 
cuit, such as that shown in Fig. 48, can be made to 



generate spontaneous oscillations, if it be so arranged 
that any change in grid voltage makes a change in 
plate current of such magnitude that there is induced 

162 












TUBE AS GENERATOR 163 


in the grid circuit a larger voltage than that originally 
acting. It has already been pointed out that in any 
electron tube much more power is produced by varia¬ 
tions in the current to the plate than must be ex¬ 
pended in changing the grid voltage to produce these 
variations. Thus there are a great variety of circuits 
in which the plate circuit is coupled back to the grid 
circuit in such a manner as to supply this small 
power to the grid and make the surplus power avail¬ 
able for use in an external circuit in the form of con¬ 
tinuous or undamped oscillations of any frequency 
from even less than one per second to 10,000,000 or 
more per second. 

This “feed-back” action can be obtained by the 
use of direct coupling from the plate back to the grid 
circuit, by inductive coupling, or by electrostatic coup¬ 
ling. The only requirement for continuous oscillations 
is that the voltage induced in the grid circuit must 
vary the plate current through an amplitude which 
supplies to the external or coupling circuits power 
sufficient or more than sufficient to maintain this volt¬ 
age in the grid circuit. 





164 TEXT BOOK ON RADIO 



Fig. 52—Radiotron Power Tube Circuit 









































WHAT HAPPENS IN A RECEIVING SET 


The aerial is placed in such a position that it can 
pick np or catch the radio waves (electro-magnetic 
waves), these waves having been set in motion at the 
transmitting or broadcasting station and travel from 
this station through space at the rate of 186,000 miles 
per second. As soon as these waves set up oscillations 
in the receiving aerial, a current is passed from the 
aerial down the lead-in wire to the primary coil of the 
transformer. The action of the current in this coil 
sets up a magnetic field; this current is induced into 
the secondary coil of the transformer and this pro- 


Atm al 


PfiimM stcogoMy 

COIL CO/U 



Fig. 53 


duces a radio frequency current which is gradually 
built up by adjusting the primary and secondary in 
electrical resonance. The variable condenser is placed 
in the circuit to allow the secondary circuit to be ad¬ 
justed to resonance with the primary circuit and also 

165 


















166 TEXT BOOK ON RADIO 


to allow of close adjustment. The induced current 
will overflow to the detector circuit as soon as the sec¬ 
ondary circuit has been put in resonance with the 
primary circuit. The detector will then rectify this 
current by transforming the high frequency to low 
frequency. The current then passes to the condenser, 
where it is stored; as soon as a single wave train has 
accumulated in the condenser the condenser will dis¬ 
charge the current into the phone receivers, where by 
its action in vibrating the diaphragm it makes the 
magnetic waves received by the aerial audible to the 
ear. 

Tuning 

The apparatus for tuning a receiving set consists of 
an adjustable circuit containing variable capacity and 



Enclosed or Cartridge Fuse 



Section of Enclosed Fuse 


Fig. 54 

inductance. The operation of the tuning apparatus is 
very simple. We have already seen that this ap¬ 
paratus is used to vary the wave length of the re¬ 
ceiving set, making it receptive to incoming signals. 

















































TUNING 


167 


As in order to receive signals, the receiving set must 
be adjusted so that the receiving circuits are in tune 
with the transmitting circuits. In other words, the 
time period of oscillation must be the same in both 
the transmitting and receiving circuits. Thus should 
we desire to receive the music or speeches from a 
broadcasting station using a 360 meter wavelength, 
then it would be necessary for us to adjust our re¬ 
ceiving set to as near that wavelength as possible to 
get maximum results. 

What Is Meant by Wavelength 

Electro-magnetic waves like light waves travel at 
the rate of 186,000 miles or 300,000,000 meters per 
second, if w r e are using an alternating current of 
25,000 cycles per second and cause a disturbance in 
the air of that frequency then each cycle will travel 
from the aerial through space at the rate of 300,- 
000,000 meters per second. So that at the end of the 
second, just as we are causing the last of the 25,000 
disturbances the first cycle or disturbance is 300,- 
000,000 meters away. In one second we have made 
25,000 separate disturbances, which have traveled 
300,000,000 meters, each disturbance separated by the 
number of meters, that 25,000 divided into 300,000,000 
will give—300,000,000 divided by 25,000 equals 12,000 
meters—it is this distance between the separate, dis¬ 
turbances that is known as the wavelength. 

Rule for Wavelength 

Add the length of the aerial to the lead-in wire. 
Add to the sum the ground and if more than one wire, 
one-third of length of aerial. Divide this total by two 
and add the result to the addition above. The answer 






168 TEXT BOOK ON BADIO 


will give the approximate wavelength in meters. 
Example: 

Length of aerial 100 feet, length of ground wire 
40 feet, length of lead-in wire 20 feet; 100+40+20= 
160 feet. One-third of 100=33+160=193; 193-^2= 
96; 193+96=284, which is the approximate wave¬ 
length in meters. 





RECEIVING SETS 


While the installation and operation of a receiving 
set is a simple matter, it means more than the con¬ 
nection of aerial and ground wires, and adjusting of 
the head phones. Thousands of owners of receiving 
sets are receiving the daily concerts, etc., but they 
are not getting the maximum results from the sets. 
The various makes of receiving sets each have their 
own characteristics, and we approached the manu¬ 
facturers with the request that they supply us with 
the information necessary to help obtain the best 
results out of their instruments. On the following 
pages we describe the construction, operation and care 
of these sets, and would ask that these directions be 
followed. The writer of this book will be pleased to 
help solve your radio troubles if you will write him 
direct, in care of the publishers. 

Apparatus for Reception of Waves 

Receiving sets are divided into two general classes, 
those suitable for the reception of damped waves and 
undamped waves modulated at an audible frequency 
and those suitable for the reception of unmodulated 
undamped waves. The former involve the simpler 
construction, and will be discussed first. With a few 
modifications, a set for receiving damped waves can 
be adapted to receive unmodulated undamped waves. 
Damped waves may be received in a simple circuit 
containing a crystal detector or simple electron tube 
detector and a telephone receiver. The tone heard 

169 


170 


TEXT BOOK ON BADIO 


in the telephone receiver is that corresponding to the 
frequency of the groups of damped waves. Undamped 
waves are ordinarily received by an electron tube 
method which produces beats. 

The fundamental principle of reception of signals 
is that of resonance. If the receiving circuits are 
tuned to oscillate at the same natural frequency as the 
incoming waves, then these waves, though extremely 
feeble, will after a few impulses build up compara¬ 
tively big oscillations in the circuits. In reality, then, 
for reception of signals all that is needed is an antenna 
circuit tuned to the same wave lengths as that of 
the transmitting station and an instrument capable of 
evidencing the current which flows in the antenna- 
connecting wire. This is shown in Fig. 55. This is the 
simplest possible arrangement for reception and will 
operate on either damped or undamped waves. A cur¬ 
rent-indicating instrument is shown at A. In practice 
the current is too feeble for any hot-wire ammeter. 
An ammeter is more suitable for quantitative measure¬ 
ments than for receiving telegraphic signals, since the 
dots and dashes are not readily distinguished unless 
made so slowly as to be impracticable for transmitting 
messages. 

A telephone receiver having magnet windings con¬ 
sisting of a large number of turns of fine wire is a 
much more sensitive receiving device. The dia¬ 
phragm can follow the audio-frequency variations of 
current occurring in ordinary speech, but can not 
follow the very rapid radio-frequency variations. The 
effect is as if the diaphragm tried to go both ways 
at once, with the result that no observable motion takes 
place. For this reason a telephone receiver alone can 
not be used to receive radio waves. To remove this 






RECEIVING SETS 


171 


difficulty a crystal detector is put into the circuit, 
which permits current to flow in one direction but not 
in the other; or, more exactly, the current in the 
reverse direction is negligibly small compared with 
the current in the principal direction. Referring to 
the reception of damped waves, it is well to remember 
that the waves are in widely separated groups. The 
action of a crystal detector upon damped oscillations 
is shown in Fig. 45; the lower halves of the waves 





JD 


a 

Fig. 55 Fig. 56 

are drawn dotted to indicate the portion of the cur¬ 
rent that is cut off by the crystal detector. 

It is found that the cumulative effect of one group 
or trjain of waves—for instance, that due to one con¬ 
denser discharge at the transmitter—pulls the tele¬ 
phone diaphragm away from its neutral position. 
The number of such pulls per second is equal to the 
number of wave trains per second. With a 300-meter 
























172 TEXT BOOK ON BADIO 


wave having 1000 wave trains per second the radio 
frequency is 1,000,000 and the audio frequency is 
1000, or one is a thousand times as high as the other. 
The upper limit of audio frequency for the human 
ear is 16,000 to 20,000 sound waves per second, so 
that even if the telephone diaphragm could, without 
a rectifier, follow the radio frequency, the ear would 
not hear the signals. In telegraphic signaling either 
a dot or a dash lasts long enough to contain many 
wave groups, and in the telephone, where the pitch 



G 


Fig. 57 

corresponds to the spark frequency, a tone is heard 
during the length of the dot or dash. 

In Fig. 56 is shown the simplest connection for re¬ 
ception with a telephone receiver. It is suitable only 
for damped waves. At D is shown the rectifier, com¬ 
monly called a “detector,” although it detects noth¬ 
ing; it alters the waves so that the telephone can 

















RECEIVING SETS 173 


detect them. The apparatus shown receives strongest 
signals from a station transmitting waves of the same 
length, or nearly the same length, as the wave length 
of the receiving circuit. The fact that the current 
from the antenna to ground must pass through either 
the telephone or the detector, both of which have 
a high resistance, renders this circuit not very se¬ 
lective, so that it will respond to a wide range of 
wave lengths. The circuit may be tuned by inserting 
a variable inductor in series between the antenna and 
the detector, the inductance being varied to change 
the wave length. 

A simple variation of this circuit which allows fairly 
sharp tuning is shown in Fig. 57, in which the 
detector and telephone are connected at the ends of 
the tuning inductance. It is well to notice how 
simple is the apparatus actually needed for reception, 
contrary to what the uninitiated person supposes. 
Three pieces of apparatus—telephone receiver, recti¬ 
fier, and tuning coil—with a suitable antenna, are 
all that are necessary to receive effectively from 
stations transmitting damped waves. 





174 


TEXT BOOK ON RADIO 









gs. 

■ooi mfd 
V.C. 


* 'll 


\ '' 





% 


Fig. 58—Diagram of the New York “Times” Long 
Distance Receiving Set 








































































WESTINGHOUSE CRYSTAL RECEIVING 

SET 


The Aeriola. Jr. consists of a variometer, a two-sec¬ 
tion fixed mica condenser, one telephone by-pass con¬ 
denser and a crystal detector contained in a nicely 
finished wood box having a separate compartment for 
telephones, the telephones being sold with the set. 

The variometer is made of micarta tubing and has 
a minimum amount of material in the field, thereby 
reducing dielectric losses. The small mica fixed con¬ 
denser is connected in series with the antenna and 
the variometer, the small section of the condenser 
being used for the reception of wavelengths between 
190 and 300 meters and the large section for wave¬ 
lengths between 300 and 500 meters. 

The crystal and telephones are shunted across a 
certain portion of the variometer, which gives the 
greatest volume of signal. 

Operation 

Connections from each section of the small mica 
condenser are brought out to separate binding posts 
permitting a change from one wavelength range of 
the set to the other by merely changing the antenna 
from one post to the other. With the aerial ground 
and telephones connected to their respective binding 
posts it is only necessary to adjust the crystal detector 
and tune with the variometer handle until the ex¬ 
pected signal is heard. After a signal is tuned in 
further signal strength may be obtained by further 
adjustment of the detector. 

175 


176 


TEXT BOOK ON RADIO 



Westinghouse Type “T. F.” Transmitter 

























































































WESTINGHOUSE TYPE R. C. SET 


The type RC regenerative set was designed to be . 
used for operation of a loud speaker and for long 
distance reception with the use of telephones. 

Construction 

This set consists of the type RA tuner, the type 
DA detector amplifier and the type CB loading coil. 
The wavelength range of the set is 180 to 700 meters, 
with the loading coil short circuited, and 1600 to 
2800 meters with the loading coil in circuit. This 
range permits reception of amateur broadcasting, up 
to 700 meters, as well as commercial and time signals 
between 1800 and 2800 meters, with the loading coil 
in circuit. 

The tuner consists of a variable condenser and vario¬ 
meter mounted on the same shaft, as a tuning unit. 
The capacity and inductance of the circuit is thereby 
increased simultaneously and in the proper L to C 
ratio. The tuning condenser is paralleled by a three- 
plate vernier condenser for sharp tuning. A tapped 
tickler is used on the type RC set and is wound on 
the same tube and alongside of the stator winding of 
the variometer. The tickler is so tapped as to permit 
a close adjustment of regeneration, thereby securing 
maximum sensitivity. 

The amplifier used in this set consists of a socket for 
the detector tube, telephone by-pass condenser, two 
sockets for amplifier tubes, two special audio fre¬ 
quency transformers and two moulded porcelain base 

177 


12 


178 


TEXT BOOK ON RADIO 


rheostats. The detector and amplifier tubes are 
mounted on a flexible rubber shock absorbing cradle, 
which prevents audio noises due to local vibrations 
from being amplified. Three jacks are provided so 
that the detector tube, first step of amplification, or 
second step of amplification, may be used. 

The loading coil used with the set consists of two 
universal wound coils, one used as a loading induct¬ 
ance and the other as a tickler for regenerating the 
loading inductance. The two coils are mounted in a 
block moulded bakelite enclosed case which is 
equipped with a plunger type switch to short circuit 
the loading coil when using the short wavelength range 
of the set. The switch permits permanent installation 
of the loading coil on the set. The leads of the coils 
are brought out to the four legs of the switch blades, 
an extension of these blades also serves as a connection 
to be clamped under the binding posts of the set. 

An electro-static shield is used to minimize the 
capacity effect of the operator’s body, this shield is 
located on the back of the panel and is kept at ground 
potential. 

The tickler and tuning knobs are secured to Micarta 
shaft extensions, thereby further minimizing capacity 
effect of the operator’s body. The connections are 
brought out to the rear of the tuner and amplifier 
by means of extension rods, and the high potential 
connections are thereby kept away from the operator, 
avoiding the capacity effect of the body, and, de¬ 
tuning and howling, as consequent results. 

The lead from the grid inductance is connected to 
the positive side of the filament of the detector tube 
and the transformer secondary winding is connected 
to the negative side of the filament of the amplifier 






WESTINGHOUSE RECEIVING SETS 


179 































































































180 


TEXT BOOK ON RADIO 


4VT 


Gfi/OQ, 


IfeftV/EJZ 
Ce#o.\ 


F/xec/ P/afes 
* 

,, *— F/oxaS/eP/afas 

fa #/able 

COWJ3EMSER. 

A/oxable CO/i. 



Fig. 61—Westinghouse Single Circuit Type Radio Receiver 





























































































WESTINGHOUSE RECEIVING SETS 181 


tubes, with a bias of approximately one volt obtained 
by keeping a certain portion of the filament rheostat 
between the transformer winding and the filament of 
the tube. This grid bias allows a material increase 
in amplification, and is such as to cause the least 
amount of distortion in the reception of speech or 
music. 

In connecting up the Type RC set it is necessary 
to put a jumper (furnished for that purpose) be¬ 
tween the grid binding post of the tuner and the 
grid binding post of the amplifier, and also a jumper 
between the tickler binding post of the tuner and the 
tickler binding post of the amplifier. The loading coil 
is then connected between the filament post of the 
tuner and the filament post of the amplifier and be¬ 
tween the plate binding post of the tuner and the 
plate binding post of the amplifier in such a manner 
as to have the loading coil switch handle vertical and 
at the top of the cabinet. (In the absence of a loading 
coil put jumpers in between the tuner and amplifier 
to replace the loading coil.) The aerial and “A” and 
“B” batteries are to be connected to their proper 
binding posts of the set and the ground connection 
taken off of the filament binding post of the amplifier. 
If a “soft” (low vacuum) tube is used as a detector, 
do not connect more than 22 y 2 volts across the de¬ 
tector “B” battery binding posts. 

Operation 

To operate the set, plug the telephones in on the 
detector, first step of amplification or second step of 
amplification, adjust the tickler for regeneration by 
means of the tickler dial on the panel and tune by 
means of the large tuning dial on the panel until the 






182 TEXT BOOK ON RADIO 


desired signal is heard. For a finer adjustment of 
tuning it is necessary to use the small vernier dial 
to the left of the tickler dial. After a signal has 
been tuned in accurately, a further adjustment of 
the tickler for maximum regeneration will increase 
the signal strength materially. 

Care should be taken not to use too much ampli¬ 
fication. If the music or speech being received is suf¬ 
ficiently strong on the first stage of amplification, do 
not attempt to use more amplification. The use of 
more amplification would “block” the second ampli¬ 
fier tube and cause local atmospheric disturbances to 
be amplified in excess of the signal amplification. The 
blocking of the second tube causes the music or 
speech to be distorted, the amplification of atmospheric 
disturbances in excess of the amplification of signal, 
naturally does not improve the clearness of the music 
or speech received. 

When using the loading coil to secure the wave- 
length range between 1600 and 2800 meters, the 
plunger switch is pulled up. To use the set for re¬ 
ception of wavelengths between 180 and 700 meters, 
the loading coil plunger switch must be pushed down, 
thereby shortening the loading coils out of circuit. 





WESTINGHOUSE RECEIVING SETS 


183 

















































184 TEXT BOOK ON RADIO 



Fig. 63—Westinghouse Aeriola Grand 






































































AERIOLA SR. RECEIVING SET 


The Aeriola Sr., a regenerative set, was designed to 
satisfy the demand for a vacuum tube set which did 
not require a storage battery to light the filament. A 
special tube, developed by the Westinghouse Electric 
& Manufacturing Company, which requires one 1 y 2 
volt dry cell and uses .23 amperes of current to heat 
the filament and using either 20 or 40 volts as a plate 
battery, is used with this set. 

Construction 

The Aeriola Sr. consists of two variometers, the 
stator windings of each being wound on the same 
micarta tube, the distance between windings and the 
value of each stator and rotor winding being such as 
to give an even increase in regenerative control. 

One variometer is used as a tickler winding for 
securing regeneration and the other variometer serves 
as a variable inductance which is used in conjunction 
with the two sections of the small mica condenser to 
secure the wavelength range of 190 to 500 meters. 

A rheostat having the resistance ware wound on 
special fibre support and the resistance unit secured 
to a moulded porcelain base is used to control the 
filament current. 

The bulb socket is set back from the panel so as 
to allow the top of the tube to protrude through a 
hole in the panel far enough to permit removal of 
the tube, yet not so far as to prevent the lid of the 
box being closed when the tube is in the socket. 

185 


186 


TEXT BOOK ON EADIO 


Operation 

The lead from each section of the small mica con¬ 
denser has been brought out to separate binding posts 
and the wavelength range of the set is determined by 
the post to which the antenna lead is connected, one 
post being the connection to the small section of the 
mica condenser and having a wavelength range of 190 
to 300 meters and the other post being connected to 
the large section of the condenser and having a 
wavelength range of 300 to 500 meters. 

Refer to the connection diagram in the lid of the 
box and connect the antenna, ground and telephones 
to the proper binding posts of the set. Connect the 
11/2 volt dry cell to the proper binding posts, positive 
lead of the battery to the positive binding post of the 
set. Connect the plate dry battery of 20 to 40 volts 
to the proper binding posts, taking care to have the 
positive lead of the battery to the post marked posi¬ 
tive “B” battery of the set. Care must be taken 
NOT to connect the “B” battery to the filament bat¬ 
tery posts of the set, doing so would burn the fila¬ 
ment of the tube out. 

Having made the above connections properly, the 
set is then ready for operation. Turn the filament 
rheostat knob until the filament of the tube glows a 
dull red. The filament is oxide-coated and must 
NOT be burned brightly. Tune the set by means of 
the variometer handle and increase the tickler until 
considerable regeneration is obtained. Avoid using 
sufficient tickler to cause the set to oscillate when re¬ 
ceiving music or spark signals. In order to secure 
best results it is necessary to make a final adjustment 
of the tickler after the signal has been tuned in by 
means of the variometer handle. 






AEEIOLA SR. RECEIVING SET 187 



Fig. 64—Westinghouse R. C. Receiving Set 






























188 


TEXT BOOK ON RADIO 



Fig. 65—Super-Hetrodyne Receiving Set 










































































































AERIOLA GRAND 


In order to receive music or speech free of disturb¬ 
ing noises it is necessary that the signal be much 
stronger than local disturbances. It is not necessary 
that a set be extremely sensitive for such reception. 
To the contrary, it is not advisable to have a super¬ 
sensitive set, such a set would detect and amplify 
local disturbances, and a conglomeration of noises 
■would accompany the reception of music and speech. 

The Aeriola Grand Regenerative Receiving Set is 
a parlor outfit of extreme simplicity in operation. 

It consists of a nicely finished box shaped very much 
like that of the modern phonograph. The set is panel 
mounted, the panel being what would ordinarily be 
the turn table of a phonograph. This panel being 
hinged at the rear forms a false lid for the box and 
permits the apparatus to be readily inspected. The 
plate batteries are placed in retainers within the box 
alongside of the loud speaking telephone, which is 
coupled to the sound chamber of the box. The panel 
is shielded to prevent the capacity effect of the hand 
from being troublesome. 

The four vacuum tubes and four ballast resistance 
tubes are mounted so as to protrude far enough 
through the panel as to be readily removed, yet not so 
far as to interfere with closing the lid. A small push 
button switch, which is in the filament battery supply 
line, is located on the panel. 

The tuning system consists of a fixed capacity, in 
the form of a small mica condenser, and a variometer 

189 


190 


TEXT BOOK ON RADIO 


which serves as a variable inductance, the handle of 
the variometer being located on the panel for tuning. 
The set is regenerative, due to a coil in the plate 
circuit, which is coupled to the variometer winding, 
this coil being tapped and pre-adjusted at the time 
of installation to give proper regeneration, no adjust¬ 
ment being provided from the panel. 

One detector tube and three resistance coupled am¬ 
plifier tubes are used in this set. The detector tube 
naturally serves as the rectifier and its grid is so 
maintained at a negative potential as to give the best 
rectification possible. The grids of the amplifier 
tubes are maintained at a constant D.C. potential 
with respect to the filament as to give the greatest 
amplification possible without distortion. 

The last amplifier coupling resistance is shorted 
by a condenser and coil in series which has been pre¬ 
calibrated to the natural period of the loud speaking 
telephone, thereby lowering the telephone amplifica¬ 
tion of the audio note at the frequency which the 
telephone would respond to most strongly and keep¬ 
ing the efficiency of the loud speaker more uniform 
for all frequencies. 

In order to simplify this set as much as possible, the 
filament rheostats are omitted and a separate ballast 
resistance tube placed in series with each filament. 
The ballast resistance consists of a certain length of 
iron wire in an atmosphere of hydrogen. The wire 
supported and the hydrogen gas maintained in a 
glass casing resembling a vacuum tube, but having 
two pins for contact on the base instead of the cus¬ 
tomary four. The function of the ballast resistance 
being to maintain a predetermined filament current 
throughout a wide range in voltage of the filament 
battery. 





THE DETECTOR 


One of the most important parts of the receiving 
set is the detector. The human ear cannot record 
frequencies above 15,000 cycles, and as we have al¬ 
ready been shown that the cycles in radio work are 
very high, sometimes running as high as 1,500,000 
cycles per second, it will be readily seen that some 
apparatus must be introduced to reduce the extremely 
high frequency used in wireless work to a frequency 
that will be audible by using the telephone -receivers. 

There are many forms of detectors. We shall first 
deal with the crystal type, which up to a few months 
ago was the one most commonly used. Crystal recti¬ 
fiers consist of certain metal compounds having the 
property of rectifying the high frequency oscillations. 

Galena (a sulphide of lead) is the mineral mostly 
used today. 

The construction and operation of a crystal de¬ 
tector is simplicity itself. On a wood base mount a 
small piece of galena between two adjustable contacts 
in such a manner that the most sensitive part of the 
crystal can be easily located by searching the surface 
of the mineral with the end of a thin (catwhisker) 
wire. 

Crystals must be kept clean to retain their sensi¬ 
tiveness. Washing with alcohol greatly improves 
them if they have been left standing without use for 
any length of time. 

Crystal Detector 

The type DB crystal detector was designed by the 
Westinghouse Electric & Manufacturing Company to 
fulfill the needs of amateurs and novices. This crys- 


191 


192 


TEXT BOOK ON RADIO 


tal detector consists of two sets of crystals with a 
switch to throw from one to the other. Necessary 
binding posts are provided for connecting the de¬ 
tector to the receiving set and to the telephones. 

One set of crystals are of the heavy contact type, 
providing a stable adjustment. 

These crystals abound with sensitive points and 
require no skill whatsoever to adjust. 

The other set of crystals consist of a fixed crystal 
of tested galena and an adjustable catwhisker tipped 
with a special composition bead. This is a relatively 
light contact detector and super-sensitive. A signal 
may be detected on the heavy contact set of crystals 
without difficulty in making the adjustment and if 
greater volume is desired the switch may be thrown 
to the super-sensitive crystals and further adjust¬ 
ments made there. 




INSTRUCTIONS FOR THE INSTALLA¬ 
TION AND OPERATION OF GREBE 
SHORT-WAVE REGENERATIVE RE¬ 
CEIVERS 


Installation 

The receiver should be placed in a position con¬ 
venient for operating control. Connect the Antenna 
and ground leads to the terminals so marked. Con¬ 
nect a 6.-volt storage battery to the terminals marked 
“ Filament Battery. ” Connect a 22 y 2 volt battery 
unit to the terminals marked “Plate Battery.” 

Make certain that all battery leads are connected 
to the proper terminals and that the polarities are 
not reversed. Connect the telephones, or amplifier 
unit, to the terminals marked “Output.” Turn the 
rheostat wheel to the “off” position and place the 
vacuum tube in the socket. The rheostat may now 
be rotated to 2. 

Operation 

To tune the receiver to a given wavelength, the 
Antenna Inductance Switches and the Grid Vario¬ 
meter must all be adjusted to that wavelength, and 
the Wavelength Range Wheel set in the position in¬ 
dicating the upper limit of the wavelength band in 
use. 

The figures opposite the contacts of the Antenna 
Inductance Switches represent the number of turns 
in the antenna circuit. Divide the wavelength desired 
by 14 to find the approximate number of turns to use. 

193 


13 



194 TEXT BOOK ON RADIO 


The Plate Variometer Dial controls the regenera¬ 
tive action and its proper setting for spark signals 
is best determined by advancing the dial until the 
signal is of maximum audibility without distortion. 
For C. W. signals, the dial must be advanced beyond 
this point, i. e., until oscillations occur—a condition 
easily recognized by a soft hissing sound in the tele¬ 
phones. The Coupler should be set at 50 for pre¬ 
liminary tuning and finally adjusted to tune out in¬ 
terfering signals. 

As many signals are inaudible until the regenera¬ 
tive action takes place, it is advisable to adjust the 



Grid and Plate Variometers simultaneously, and make 
final adjustment of Antenna Inductance for maximum 
signal strength. The tangent-wheel verniers are indis¬ 
pensable in accurately turning all weak signals, espe¬ 
cially C. W. and telephones. 

Location of Faults: 

(a) If adjustment of Plate Variometer fails to 
profuse regeneration, adjust filament current, plate 
voltage, or both. 

(b) If adjustment of Plate Variometer produces 
regeneration but no appreciable increase in signal 







































LOCATION OF FAULTS 195 


strength, adjust Antenna Inductance, Coupling, or 
both. 

(c) If vacuum tube filament fails to light, or flick¬ 
ers, remove the tube and clean the end of its four 
contacts with a file or sand-paper. 

(d) Grinding noises are caused by: 

1— Faulty Connections. 

2— Defective Plate Batteries. 

3— Defective Vacuum Tubes. 

Unlike static disturbances, these noises persist when 
the antenna is disconnected, and they may be elimi- 



Fig. 67 —Circuit for Reception of Modulated C. W. Signals 

nated by tightening binding posts, cleaning the ends 
of the vacuum tube contacts, or replacing defective 
tubes or batteries. 


Type CR-3 

The operation of the Type CR-3 is essentially the 
same as the CR-8, with the exception that the detector 
is not included in the set. Four terminals are pro¬ 
vided for externally connecting the detector unit. 
The combination of the Type CR-3 Receiver with the 
Type Rork detector-amplifier represents a complete 
receiving station equipment, the detector-amplifier 











































\ 


196 TEXT BOOK ON RADIO 


unit being also available for use with other receiving 
circuits. 

The Type CR-8 Receiver in combination with the 
Type Rork Two-Stage Amplifier unit is a complete 
station equipment in which the two stages of amplifi¬ 
cation are available for use with other receiving cir¬ 
cuits. 



Fig. 68—Armstrong High Frequency Amplifier Circuit 


Dr, 




V V • 


V 


















































INSTRUCTIONS FOR THE INSTALLA¬ 
TION AND OPERATION OF GREBE 
INTERMEDIATE-WAVE REGENERA¬ 
TIVE RECEIVERS 

Installation 

The receiver should be placed in a position conveni¬ 
ent for operating control. Connect the Antenna and 
ground leads to the terminals so marked. Connect a 
6-volt storage battery to the terminals marked 
“Filament Battery.” (Connect two 22%-volt bat¬ 
tery units in series). Connect the junction of these 
batteries to the terminal marked “Detector.” Con¬ 
nect the ends of these batteries to the remaining 
terminals marked “Amplifier.” 

Make certain that all the battery leads are connected 
to the proper terminals and that the polarities are 
not reversed. Connect the telephone terminals to one 
of the plugs supplied with the set. 

Turn all .three rheostat wheels to the “off” posi¬ 
tion and place the vacuum tubes in the sockets. In¬ 
sert the telephone plug into the jack marked “De¬ 
tector,” and turn the detector rheostat wheel to 2. 

Operation 

Combinations of antenna inductance and antenna 
series capacity as indicated by the Inductance Switch 
and the Condenser Dial, result in the wavelength 
shown for these combinations on the Wavelength 
Chart. The Tickler Dial controls the regenerative 
action and its proper setting for spark signals is best 

determined by advancing the dial until the signal is 

197 


198 


TEXT BOOK ON BADIO 


of maximum audibility without distortion. For C. W. 
signals the dial must be advanced beyond this point, 
i. e., until oscillations occur, a condition easily recog¬ 
nized by a soft hissing sound in the telephones. 

As many signals are inaudible until regenera¬ 
tive action takes place, it is advisable to adjust the 
Condenser and Tickler Dials simultaneously. The 
Vernier Wheels are essential in accurately tuning all 
weak signals, especially C. W. and telephones. 

After tuning and detector adjustments have been 
made, the telephone plug may be changed to the First 
Stage Amplifier position and the corresponding rheo¬ 
stat adjusted for maximum signal strength. The 
same procedure is followed in adjusting the second 
stage. When it is desired to use a loud-speaker this 
instrument should be connected to the terminals 
marked “ loud-speaker, ” and the telephone plug in¬ 
serted into the second stage just far enough to light 
all three filaments. 

When it is desired to use the amplifier section in 
conjunction with external tuning and detector ap¬ 
paratus, connect the output of the external detector 
to the other plug supplied with the set. Also connect 
the filament leads of the external detector to the 
terminals marked “external filament.” Thus, when 
the plug is inserted into the jack marked “External 
Detector,” the automatic control device will cause 
the external filament to be lighted and the filament 
of the detector tube in the CR-9 to be extinguished. 

Location of Faults 

(a) If adjustment of Tickler fails to produce re¬ 
generation but no appreciable increase in signal 
strength, adjust Condenser. 






GREBE RECEIVING SETS 199 


(b) If vacuum tube filaments flicker or fail to light 
remove the tubes and clean the ends of their contacts 
with a file or sand-paper. If this does not eliminate 
the trouble, it may be necessary to adjust the filament 
control blades of jacks. 

Remove all plate battery connections before making 
these adjustments, to prevent short circuit resulting 
in the burning out of vacuum tube filaments. 

(c) If both stages fail to product amplification, the 
trouble may be traced to faulty plate batteries, or re¬ 
versal of the filament battery leads. Defective tubes 
cause the majority of other troubles. It is desirable 
to try the tubes in various combinations for detector, 
first and second stages. 

Grinding noises are caused by: 

1— Faulty connections. 

2— Defective plate batteries. 

3— Defective vacuum tubes. 

Unlike static, these noises persist when the antenna 
has disconnected and they may be eliminated by 
tightening binding posts, cleaning the ends of vacuum 
tube contacts or replacing defective tubes or bat¬ 
teries. Type CR-5—The operation of the CR-5 Re¬ 
ceiver is essentially the same as the type CR-9 with 
the exception that the amplifiers are not included. 

The Type CR-5 Receiver in Combination with the 
Type Rork Two-Stage amplifier is equivalent to the 
Type CR-9. 





200 TEXT BOOK ON RADIO 



Fig. 69 





















TUNING METHOD FOR THREE CIRCUIT 

RECEIVERS 

While excellent results may be obtained with ap¬ 
proximate adjustments, the additional effort required 
for careful tuning is justified by the greatly im¬ 
proved reception, and in order to obtain maximum 
signals it is necessary to tune each of the three cir¬ 
cuits to the wavelength of the desired signal. In all, 
there are five separate adjustments to be made. 

1— Primary circuit (Antenna Inductance). 

2— Secondary circuit (Grid Variometer). 

3— Coupling (Coupler). 

4— Plate circuit (Plate Variometer). 

5— Detector (Vacuum tube). 

Failure to make all the adjustments results in in¬ 
audibility of weak or distant signals, instability of 
audible signals, distortion of radiophone speech or 
music, due to improper amplification. 

Tuning for Signals of Unknown Wavelength. 

Set the grid variometer dial to correspond with the 
desired wavelength. 

Set the coupler dial to either 50 position. 

Starting from the zero position gradually increase 
the plate variometer dial to the point where oscilla¬ 
tions occur. (This condition is recognized by a soft 
hissing sound in the telephones.) 

201 



202 


TEXT BOOK ON RADIO 


Adjust the antenna inductance switches to a com¬ 
bination which causes the cessation of oscillations. If 
a Variable Antenna Series Condenser is used, adjust 
the switches to a combination which will cause the 
oscillations to cease upon rotation of the condenser 
dial to some point between 70 and 90. 

The desired signal should now be audible in the 
telephones and final adjustments may be made with 
the grid variometer and coupler. The use of the 
tangent wheel verniers is essential is making these 
final adjustments. 

Set the coupler on either 50 position. 

Make approximate adjustment of the antenna in¬ 
ductance switches, setting them at a higher rather 
than a lower wavelength than is expected. 

Using both hands, simultaneously rotate the grid 
and plate variometer dials over the entire scales. The 
dials should be rotated so as to keep the circuits or 
the verge of oscillating. 

When the desired signal has been located on the 
grid variometer dial rotate the coupler dial toward 
zero until the signal is barely audible and then adjust 
the primary circuit. 

Make a final adjustment on the Coupler dial. 


TUNING METHOD FOR TWO CIRCUIT 

RECEIVERS 

The tuning of this type of receiver is more simple 
than the three circuit type. Maximum signal is ob¬ 
tained only when the wavelength control circuit is ad¬ 
justed to the same wavelength as the desired signal, 





TUNING 


203 


and the tickler is adjusted to the point of greatest 
amplification. 

Tuning for Signals of Known Wavelength. 

Set the inductance switch for the desired wave¬ 
length range. 

Set the condenser dial to the position correspond¬ 
ing to the wavelength desired. 

Starting* at zero gradually increase the Tickler dial 
reading to a position just below the oscillating point. 
(The oscillating condition is indicated by a soft hiss¬ 
ing sound in the telephones.) 

The desired signal should now be audible in the 
telephones and final adjustments may be made with 
the tangent wheel verniers. 

Tuning for Signals of Unknown Wavelength. 

Set the inductance switch in the position corre¬ 
sponding to the range in which the signal is expected. 

Using both hands simultaneously adjust the con¬ 
denser and tickler dials over the entire range, main¬ 
taining the proportion necessary to keep the receiver 
on the verge of the oscillating condition. If the sig¬ 
nal occurs below 10 on the condenser dial, move the 
inductance switch to the next lower point, and if the 
signal occurs above 90, move the inductance switch 
to the next higher point. 

SPECIAL TUNING INSTRUCTIONS 

Spark Signals 

The reception and amplification of spark signals 
will be most satisfactory when the regenerative action 





204 


TEXT BOOK ON RADIO 


is controlled to a degree which will produce maximum 
amplification without causing an oscillating condition 
in the circuits. When the oscillating • condition is 
reached, the tone of the spark signals will be de¬ 
stroyed and reception through interference will be¬ 
come almost impossible. 

Modulated C. W. Signals 

Modulated C. W. Signals, including I. C. W. Buzzer 
Modulated C. W. and Voice, may be received in a 
like manner, but a special condition may be obtained 
by allowing oscillations to take place in the receiver, 
producing the exact frequency of the incoming wave¬ 
length. This is known as the “zero beat” method and 
in this condition amplification is greatly increased due 
to the augmented feed-back of energy from the plate 
to the grid circuit. It is only possible to make use 
of this method while incoming frequency remains 
constant and its successful application requires con¬ 
siderable skill. 

C. W. 

In the reception of continuous waves the plate cir¬ 
cuit feed-back is to be increased to a point where 
oscillations are constantly taking place and this con¬ 
dition must be maintained throughout the entire tun¬ 
ing operations. 

Receivers Used as Wavemeters. 

The wavelength of incoming signals or of any local 
oscillating circuit may be determined by noting the 
grid variometer dial setting. This applies to the 
CR-8 Receiver and the CR-3 Rord combination. 
Where the CR-3 Receiver is used in conjunction with 




ELIMINATION OF INTERFERENCE 205 


non-standard detecting apparatus, the readings will 
be inaccurate. The wavelength of local oscillating 
circuits may be obtained with the CR-5 or CR-9 Re¬ 
ceivers by shunting the antenna and ground binding 
posts, noting the Condenser dial reading. 

Elimination of Interference 

The most successful means for reducing spark in¬ 
terference while receiving modulated C. W. signals 
is the use of the zero beat method described above. 
This will cause the spark signal to become distorted 
and suppressed while greatly increasing the amplifi¬ 
cation of the desired signal. 













































206 


TEXT BOOK ON RADIO 


Eliminating interference from spark and modulated 
C. W. signals while receiving C. W. signals. 

As the oscillating condition is a pre-requisite in the 
reception of C. W. signals, it follows that spark signals 
are more readily suppressed than are the modulated 
C. W. signals. Where the carrier wavelength of the 
modulated C. W. signal and the wavelength of the 
desired signal are almost identical it will only be 
possible to suppress the modulated C. W. signal is 
beyond audibility. In the Types CR-3 and CR-8 re¬ 
ceivers, an additional freedom from spark interfer¬ 
ence is to be gained by the use of the coupling ad¬ 
justment. 

The elimination of C. W. signals while receiving 
spark signals is easily accomplished by reducing the 
plate variometer or Tickler dial setting until the 
oscillations cease, unless the C. W. station is very 
powerful and located nearby. 



Fig. 71—Tuned Plate Regenerative Circuit, Using Variable 

Inductances 




















INSTALLATION OF DETECTOR AND 
TWO-STAGE AMPLIFIER 


The Detector-Amplifier unit should be placed as 
close to the receiver as possible in order to avoid 
lengthy leads. The four terminals on the left are 
provided for externally connecting the amplifier with 
the receiver. 

Connect a 6-volt battery to the terminals marked 
“Filament Battery.” 

Connect two 22 !/ 2 - v olt battery units in series. Con¬ 
nect the junction of these batteries to the terminal 
marked “Detector.” Connect the ends of these bat¬ 
teries to the terminals marked “Amplifier.” 

Make certain that all battery leads are connected 
to the proper terminals and that the polarities are 
not reversed. 

Connect the telephone terminals to one of the plugs 
supplied with the unit. 

Turn all the rheostat wheels to the “Off” position, 
and place the vacuum tubes in the sockets. 

Insert the telephone plug in the jack marked “De¬ 
tector” and turn the detector rheostat wheel to 2. 

Operation 

After tuning and detector adjustments have been 
made, the telephone plug may be changed to the 1st 
stage amplifier position and the corresponding rheo¬ 
stat adjusted for maximum signal strength. The same 
procedure is followed in adjusting the 2nd stage. 

207 


208 TEXT BOOK ON RADIO 


When it is desired to use a loud speaker, this in¬ 
strument should be connected to the terminals marked 
“Loud Speaker” and the telephone plug inserted in 
the second stage jack just far enough to close the 
filament circuit of all three tubes. 

When the amplifier section is used with external 
tuning and detecting apparatus, connect the output 
of the external apparatus to a telephone plug. Also 
connect the filament leads to the terminals marked 
“External Detector.” Thus, when the plug is in¬ 
serted in the jack marked “External Detector” the 
automatic control device will cause the external de¬ 
tector tube filament to light and the detector tube fila¬ 
ment in the Rord will be extinguished. 

Location of Faults 

(a) If vacuum tube filaments flicker or fail to light, 
remove the tubes and clean the ends of the contacts 
with a file or sandpaper. If this does not eliminate 
the trouble, it may be necessary to adjust the auto¬ 
matic control jacks. 

Remove all Plate Battery connections before mak¬ 
ing jack adjustments to prevent short circuit resulting 
in the burning out of vacuum tube filaments. 

(b) If both stages fail to produce amplification, 
the trouble may be traced to faulty plate batteries, or 
the reversal of the filament battery leads. Defective 
tubes cause a majority of other troubles. It is desir¬ 
able to try the tubes in various combinations for de¬ 
tector, 1st and 2nd stage. 

Installation of Two-Stage Amplifier 

Connect a 6-volt storage battery to the terminals 
marked ‘ ‘ Filament Batterv. ’ ’ 





OPERATION 


209 


Connect two 22^-volt battery units in series; con¬ 
nect the ends of these batteries to the terminals 
marked “Plate Battery.” 

When this amplifier is used with the Grebe Type 
CR-5 or CR-8 Receiver, a connection may be made 
from the junction of the two 22%-volt batteries to 
the Plate Battery Terminal on the receiver. With 
this circuit a single plate battery is made to serve both 
units. No connection need be made to the “Plate 
Battery” terminal on the receiver as this cir¬ 
cuit is completed through the positive side of the Fila¬ 
ment Battery which is common to both Receiver and 
Amplifier. Connect the “Filament Battery” termi¬ 
nals of the receiver to the “External Filament” termi¬ 
nals of the amplifier. Connect the output or tele¬ 
phone terminals marked “Input” on the amplifier. 


14 





REGENERATIVE RECEIVING SETS 


A regenerative, or feed back receiving set, is one in 
which the oscillations received from the aerial are 
regenerated by the action of the current in the vacuum 
tube. 

The advantages of the vacuum tube set over the 
crystal set are many. It is much more sensitive, per¬ 
mits of finer tuning, and the tuning out of interfer¬ 
ence; through the regeneration in the vacuum tube 
the incoming signals are greatly amplified, and then 
one or more stages of amplification can be added to 
the set at will. 

It is, naturally, the desire of all radio fans to own 
a regenerative receiving set, but the cost of same is 
generally more than they care to invest; however, 
by buying the various parts and assembling the set 
oneself the cost can be materially reduced. In fact, 
a vacuum tube set can be assembled in this way for 
approximately Thirty Dollars. 

The inductance coil and tickler are the only parts 
of this set that I would suggest building. It will 
be found just as cheap to buy the other parts com¬ 
plete. 

To make the inductance coil, secure 2 cardboard 
tubes, one 8 inches long by 3y 2 inches in diameter, the 
other iy 2 inches long by 2% inches in diameter. 
First dry the tubes by placing in a warm oven for 
about an hour and then giving them, inside and out, 
a coat of shellac. On the larger tube wind about 6 

210 


INDUCTANCE COIL 


211 


inches of its length with No. 24 cotton covered wire, 
taking a tap off every tenth turn up to the 80th 
turn, and then a tap off every 40th turn after. This 
winding acts as the antenna tuning inductance. The 
tickler coupler winding is wound on the same tube 
and consists of two sections with 20 turns of wire 
in each section. 

The flexible wires leading from the taps on the 
coil should be connected to a multipoint switch. 


CARDBOARD 'fVBE Q>lNCHesLoN$ 



<- - -• ? 


ifi UoRQ 



Fig. 72 


On the smaller tube, wire should be wound as per 
the diagram; it is now necessary to mount the small 
tube so that it can rotate within the larger one, and 
this is best accomplished by running a shaft through 
the large tube, and mounting the smaller coil on this 
shafting, similar to the diagram. 

The other parts necessary to complete the set will 
be a vacuum detector tube, vacuum tube socket, fila¬ 
ment rheostat, variable condenser, grid condenser, grid 
leak, 22-volt battery, and a six-volt battery. 

A regenerative set may also be made with the fol¬ 
lowing parts: A set of honeycomb coils (A piimai\, 
B—tickler, C—secondary), vacuum detector tube, 
variable condenser, grid leak, vacuum tube socket and 
adjustable filament rheostat, storage battery, “B” bat¬ 
tery, head phones, binding posts, nuts and screws, 



















212 TEXT BOOK ON RADIO 


a few feet of No. 18 wire and a Bakelite panel, to 
mount the whole affair on. 

Still another set ean be made by using a vario 
coupler, 2 variometers, vacuum tube, vacuum tube 
socket, filament rheostat, 6-volt battery, variable con¬ 
denser, “B” battery, multipoint switch, Bakelite 
panel, wiring nuts and volts, binding posts. 



Showing, meth on mounting Shi all con. inside The 

ONE 30 THAT /T CAN &E FOf/M’EO BY HNO & ON 
THE 0UT3WE OF TAN EL 


Fig. 73 

Parts required for a two-step amplifier: 2 amplify¬ 
ing transformers, 2 amplifying vacuum tubes, 2 
vacuum tube sockets, 2 adjustable filament rheostats, 1 
single socket telephone jack, 1 double socket telephone 
jack, 1 telephone plug, panel of Bakelite, binding 
posts, nuts and screws, etc. 

FIXED CONDENSER 

Fixed condensers are used as shunts across the 
detector to intensify the incoming signals and to pro- 




















FIXED CONDENSER 


213 


mit of fine tuning. To make a fixed condenser, first 
cut a number of strips of tin foil into sheets meas- 
uring 3 inches by 2 inches wide. Then lay two pieces 
of paraffined paper on a strip of cardboard measur¬ 
ing 3 inches long by 2 inches in width. On top of 



Fig. 74—Variometer 


these sheets of paraffined paper lay one of the strips 
of tin foil, leaving about % inch projecting over the 
end of the paraffined paper. Now, place another 
sheet of paraffined paper over this, seeing that it co¬ 
incides with the sheet of paraffined paper under it, 
and on top of this lay another strip of tin foil, this 
time letting it project % inch over the paraffined 
paper on the opposite end. And so on, the condensei 
being built with alternate layers of paraffined paper 
and tin foil, until the desired number of sheets have 
been built up. Place two pieces of paraffined paper 










214 TEXT BOOK ON RADIO 


on the top and over this a strip of cardboard, the 
same size as that at the bottom. The whole thing is 
then bound up with thread. Now, lay the condenser 
on a board fixing on two binding posts, so that they 
clamp down to the projecting ends of tin foil to the 
wood base. The condenser is then ready for use in the 
circuit. 


■Sheet of Unfoiu 


PaK AFFINED -pApgR | 

I -Para FFlNED VAPEfC 


op Tin Foil 


«f 

* 



WOOD ja/\S£. 

Fig. 75 

nfjBTBq ' 





















THE VARIABLE CONDENSER 


The variable condenser is an apparatus used in con¬ 
junction with the receiving set to make it capable of 
receiving weak signals. There are a number of types 
and models. The most common type consists of a 
number of metal plates separated from each other 
by an air-gap, or insulated from one another by sheets 
of mica, the whole being mounted in a circular case. 
One set of the plates are fixed, while the other set 



Fig. 76 


is mounted on an insulated spindle, which can be 
turned through an angle of 180 degrees, thus per¬ 
mitting of any required amount of interleafing of 
the plates. 

There are other types on the market which use 
only two plates. The one illustrated on this page is 
made up of two plates, A and B. A is fixed; the 
plate B is free to move up and down, to or from plate 
A. The surface is covered with a thin circular sheet 
of mica C, and the plate B has secured to its under¬ 
side a block of insulated material, which acts as a 


215 








216 


TEXT BOOK ON RADIO 



Fig. 77—Internal Construction of a Two-Plate Condenser 

support for the guide rod and screw. The variation 
of the capacity is obtained by merely screwing the 
rod upward or downward on the shaft, which moves 
the plate B to or from plate A. 


THE VARIOCOUPLER 

An ideal receiving set is made up of two variometers 
and one vario-coupler. To make a vario-coupler, first 
thoroughly dry and coat with shellac two cardboard 
tubes, one about four and the other about three inches 
in diameter, then wind the larger tube with about 
60 turns of No. 24 cotton-covered wire, taking a tap 
off everv tenth turn of wire. Next, take the smaller 
cardboard tube and wind about 50 turns of No. 24 
cotton-covered wire on this. The tubes now have to 
be mounted so that the small tube can rotate inside 




























THE VARIOCOUPLER 


217 



Fig. 78 

the larger one. The large coil acts as the primary, 
and the small coil as the secondary. The flexible wire 
leads from the taps on the larger coil now have to 
be connected to a multipoint switch, while one end 
of the large coil is connected to the aerial 


VARIOMETER 

A Variometer is a tuner that depends on the coup¬ 
ling between its two parts, which are connected to¬ 
gether. It generally consists of one fixed and one 
movable coil, connected in series with each other, and 
mounted so that the coupling between the two coils 
can be varied and readily adjusted. The inductance 
of the combination is changed by varying the relative 
position of the coils. There are a number of different 








218 TEXT BOOK ON BADIO 


types on the market all meeting with more or less 
success. One of the best is the basket-weave type of 
winding on spherical forms. This type can be 



Fig. 79—180° Yarioeoupler 


mounted in any desired position. The variometer 
should not be connected in series with the secondary 
of the loose coupler; this adds resistance to the cir¬ 
cuit and weakens the signals. The working principles 
of a variometer are the same as an inductance, or 
tuning coil. 


LOOSE COUPLER 

A loose coupier is used in place of a tuning coil. 
With it, one can get a greater selectivity. It consists 
of 2 coils, the primary and the secondary, the second- 





LOOSE COUPLER 


219 


ary being so constructed that it will slide in or out 
of the primary. 



Fig. 80—Basketball Variocoupler 


First, thoroughly dry 2 cardboard tubes, one about 
8 inches long, by 4 inches in diameter, and the other 
about 7 inches long by 3% inches in diameter. Wind 
the larger tube, which will act as our primary, with 
a layer of cotton covered wire, starting y 2 inch from 
one end of the tube, and finishing y 2 inch from the 



- a 


HoLt 1 foK 


'7 > /vmar</ Coil. 


V 

— 4 - 


fioic ju if L^RCC 



Fig. 81 











220 TEXT BOOK ON BADIO 


other end. Now give the whole thing a coat of shellac, 
inside and out, and lay aside until dry. Take the 
smaller tube and wind this with No. 24 cotton covered 
wire, starting y 2 inch from the end and finishing 



y 2 inch from the other end. When winding this 
tube, which will be our secondary, it will be necessary 
to take a tap about every inch of winding. This is 
done by punching a small hole in the tube and pushing 


J9 ft A S S 7fo_0 W/<« Si-ZD/A/C, CoNlat'f. 



Fig. 83 





































LOOSE COUPLER 


221 


the wire through, inside the tube, allowing us to 
make the taps from the inside, instead of the out¬ 
side. 

These taps are connected to contact points on tne 
wood end piece, and the end of the coil should also 
be led to one of these contact points (see Fig. 82). 
The other end of the winding (the beginning), should 
be connected to the binding posts. 

It will thus be seen that by rotating the adjust¬ 
ment handle on the end piece, that more or less of 



the secondary winding can be cut in or out of the 
circuit. 

Be careful when winding the coils that the wires 
are wound on both coils in the same direction. 

We shall now need two pieces of wood about 5 
inches square and a wood disc just large enough to 
tit into the end of the larger coil. One of the square 
w r ood pieces must have a hole cut out the center, 4 
inches in diameter; we shall also need a wood base 
18 inches long by 6 inches in width, 2*4 inches in 

























222 


TEXT BOOK ON EADIO 


brass rods, 17 inches long and one brass rod 8 1 /? 
inches long. 

Secure the wood disc onto the center of the end 
piece, then slip this into the end of the larger tube, 
the other end of the tube is slipped into the hole 
of the other end piece (Fig. 83). 

Now secure the guide or travel rods by passing them 
through the secondary coil and then through the pri¬ 
mary coil, and slip the ends into the two holes made 
for them in the wood disc; the other ends are secured 
to a small block of wood, which in turn is fastened 
to the wood base. The secondary coil is now pushed 
into the primary, and the whole affair mounted onto 
the base. The small brass rod with a sliding contact 
should now be mounted between the two end pieces 
over the primary coil in such a manner that the slider 
makes good electrical contact with the wiring of the 
coil. 

The operation of this set is simple; push the sec¬ 
ondary coil right into the primary, and tune as you 
would with an ordinary tuning coil; when the signal 
is heard, move the switch on the end of the secondary 
coil till you get maximum result. Then adjust the 
various condensers, to try and better the signal’s 
strength. Next, slowly draw out the secondary coil 
and retune, repeat this process until you get the maxi¬ 
mum signal strength. 


DOUBLE SLIDE TUNER 

First secure a cardboard tube about 8 inches in 
length, by S 1 /* inches in diameter. This tube should 
be placed in a warm oven for an hour or so, and then 








DOUBLE SLIDE TUNER 


223 


given 2 coats of shellac, wait till the first coat is hard 
and dry before applying the second. Next, wind the 
tube with No. 25 B & S gauge cotton covered wire, 
starting about % inch from one end of the tube, and 
finishing about the same distance from the other end. 
Now give the tube another coat of shellac (inside and 
out) and lay aside until dry. 


<- 


£ 


'BRASS'RoJD SQUARE 


snoop vises just large enough to 

FIT INTO tube 






CARDBOARD TUBE 8 FONG 
IRJJ/AMETER 

BRASS ROD /u* SQUARE 9 * FONG 



£ 


SLIDING CONTACT" LARGE ENOUGH T o 

FIT OVER BRASS Ron 


Fig. 85—Units of Double Slide Tuner 


Next secure 2 pieces of wood about 4 inches square 
and V 2 inch thick, and 2 wood discs just large enough 
to fit into the ends of the cardboard tube. First 
mount these discs in the center of the wood end pieces, 
and then slip the ends of the cardboard tube over 
the discs, then nail the tube onto the discs. 

We shall now need 2 brass rods about % inch 
square, by 9 inches long, and 2 sliding contact points. 
The contact points are placed on the rods (see dia¬ 
gram) and the 2 rods are fastened, one on the top, 


























.224 


TEXT BOOK ON RADIO 


and one on the side of the coil, in such a manner 
that the sliding contact points can be worked along 
the whole length of the rods, making sure that the 
contact points make good electrical connection with 
the wire on the cardboard tube. It will be found 
necessary to scrape the wire where the sliding contact 



Fig. 86 


points work to get good electrical connection. A sim¬ 
ple hook-up is here given, showing how this tuner 
is connected into the circuit. The other apparatus 
necessary for the outfit consists of a variable con¬ 
denser, a fixed condenser, and a crystal detector. 

HOW TO MAKE A TUNING COIL 

A simple tuning or loading coil consists of a card¬ 
board tube, around which a wire is wound, and so 
arranged that more or less of this wire can be cut in 
or out of the circuit by means of a sliding contact 
point. To build the coil you will need the following: 
A cardboard tube 18 or 20 inches long and about 4 
inches in diameter, 1 y 2 lbs. of No. 24 copper wire, 2 
brass rods a trifle longer than the cardboard tube and 






























TUNING COIL 


225 


approximately y± inch square. Two wood discs, % 
of an inch thick and just large enough to fit tightly 
into the ends of the cardboard tube, two wood pieces 
for ends, about 4y 2 inches square and a wood base 
to mount the whole affair on. First wind the wire 
tightly around the whole length of the cardboard 
tube, leaving a free end of wire at each end of the 
tube. Care should be taken to space the winding 
evenly. Next, mount the two wood discs in the 
center of the two wood end pieces. Then slip the 
discs one into each end of the cardboard tube and 
mount the whole affair on the wood base. It is now 
necessary to mount the brass rods in such a manner 
that the sliding contacts on the rod makes a good 



Fig. 87—A Complete Receiving Set on a Common Base 


A—Connection to Aerial 
C—Brass Rods 
E—Sliding Contacts 
G—Crystal and Holder 
J —Fixed Condenser 


B—Wood End Pieces 
D—Connection to Ground 
F—Phone Connections 
H—Adjustable Catwhisker 
Holder 

K—Catwhisker 


15 




















226 


TEXT BOOK ON BADIO 


contact on the wire windings of the coil. One end of 
the wire windings is attached to a binding post, while 
the other end is passed through a hole in the card¬ 
board tube, so that it will be out of the way. It will 
be found advisable to dry all wood used in the build¬ 
ing of radio apparatus, by leaving it for an hour or 
two in a warm oven, then giving it a coat of shellac. 
This will eliminate shrinking or warping of the w 7 ood. 
There are various makes of coils on the market and 
I do not think it advisable to go to the trouble of 
constructing one, as long as they can be bought so 
cheaply. A number of beginners, however, like to 
build their own, and it is for them that this article 
is written. 


LOUD SPEAKERS 

To make it possible for a number of people gathered 
together in one room to hear the concerts, etc., from 
one receiving set, a loud speaker must be employed. 
The loud speaker can be termed an instrument used 
to amplify radio signals. There are various types on 
the market all meeting with more or less success. A 
diagram of the “Telemegaphone” is here shown. A 
small coil of fine wire is placed in a circular air-gap 
between the poles of a very powerful electromagnet, 
and this coil attached to the diaphragm. The mag¬ 
netic flux across this air-gap is constant, and the cur¬ 
rent is sent through the small coil. Whenever a cur¬ 
rent flows through the coil it is either attracted or 
repelled, according to the direction of flow through 
the coil, and the motion thereupon transmitted 
to the diaphragm. There are no pole pieces to in¬ 
terfere with motion, which may be as large as the 






LOUD SPEAKERS 


227 



Plate Circuit of Amplifier.) 


[Fig. 88—Telemegaphone 
















































228 TEXT BOOK ON BADIO 


elastic limit of the diaphragm. A large horn is at¬ 
tached immediately above the diaphragm, and the air 
column in that horn moved in accordance with the 
vibrations of the diaphragm. The “Vocaloud,” an¬ 
other make of loud speaker, has met with great suc- 



Fig. 89—Loud Speaker 


cess. In this instrument, a balanced armature is em¬ 
ployed, which is actuated by a magnetic field be¬ 
tween four pole pieces, the field is caused to vary in 
accordance with the audio frequency component of 
incoming signal currents as the energy is passed 
through the single solenoid. The movement of the bal¬ 
anced armature is conducted to the mica diaphragm 
by a small connecting link. 

Vocarola 

The Westingliouse Vocarola is designed to be used 






LOUD SPEAKERS 229 


with a set such as the type R.C. set. It is a scientifi¬ 
cally designed sound amplifier and when connected in 
place of the telephones of the type R.C. set will deliver 
many times the volume of a pair of telephone re¬ 
ceivers. 

A diaphragm of aluminum with concentric circular 
corrugations is used in the telephone receiver of the 
Vocarola. The corrugations stiffen the diaphragm and 
prevents it from vibrating with nodal patterns. As 
a result there is only one free period. The Vocarola, 
therefore, gives an excellent quality of reproduction 
for the reception of both music and speech. 

Victrola Attachment 

The Westinghouse Victrola or Grafanola attach¬ 
ment employs the same telephone receiver as the Voca¬ 
rola and is provided with an attachment which per¬ 
mits its replacing the reproducer of the phonograph 
and thereby utilizing the sound chamber of the 
phonograph. 



Fig. 90—Westinghouse Loud Speaker 





230 


TEXT BOOK ON BADIO 




\ 

jiskii 



Fig. 91 


























ARMSTRONG SUPER-REGENERATIVE 

CIRCUIT 


Major E. II. Armstrong, who is already well known 
to all radio fans throughout the world, is responsible 
for a new Super-Regenerative Circuit. A successful 
demonstration of this circuit was given by Mr. Arm¬ 
strong at a meeting of the Institute of Radio Engi¬ 
neers on June 7, 1922. Only three tubes were em¬ 
ployed with a loop aerial and the volume of sound 
received from Station WJZ, at Newark, N. J., was 
sufficient to fill the large meeting room in the Insti¬ 
tute. During the demonstration Mr. Armstrong 
pointed out that the building was practically radio¬ 
proof against any ordinary receiving set, using an 
indoor loop aerial. To K. B. Warner, editor of 
Q. S. T. we are indebted for the following informa¬ 
tion on the Super-Regenerative Set. 

As w r e all know from experience, oscillation repre¬ 
sents the theoretical limit of amplification in our 
present-day receivers. How often, in approaching 
critical regeneration and hearing the signals build up 
enormously, have we wished that it might be possible 
to advance the regeneration just a little more, even 
one degree on the scale, without the bulb flopping into 
oscillation! The increase in amplification just below 
the oscillating point is amazing, and if only it could 
be squeezed a wee bit more how wonderful it would 
be! That is exactly what Armstrong’s new scheme 

231 


232 TEXT BOOK ON RADIO 


does—it extends the range of regeneration without 
oscillation, by means of a trick. We say a trick be¬ 
cause the oscillating point is theoretically the limit 




but by an artifice this is got around and any amount 
of amplification may be obtained; and because it is in 








































































SUPER-REGENERATIVE SETS 


233 


a field beyond the hitherto recognized limit, it is called 
super-regeneration. 

Let us first study a few basic points regarding ordi¬ 
nary regeneration. As is well recognized, it consists 
of supplying energy by some process akin to feed¬ 
back in such a manner as to enforce the oscillations in 
the circuit, causing them to attain greater amplitude 
and thereby having the same effect as would the in¬ 
troduction of “negative resistance.’’ That is, part of 
the positive resistance which the circuit normally 
would have seems to have been overcome, we say that 
by the use of regeneration its effective resistance has 
been lowered. Now, obviously, the “negative resist¬ 
ance ’ ’ created by the feed-back may be not as great as 
the positive resistance, or it may just equal it, or it 
may be greater than the positive resistance. Let us 
examine each of these in turn: 

When the negative resistance is less than the posi¬ 
tive (which is the case in our regenerators of today), 
the oscillations in the circuit attain a steady amplitude 
of a value dependent upon the effective resistance; this 
amplitude is always finite, is reached in a finite time, 
and dies away to zero when the exciting e.m.f. is re¬ 
moved. Now when the negative and positive resist¬ 
ances are equal, the resultant effective resistance of 
course is zero. When an e.m.f. is impressed on-such 
a circuit the current builds up at a rate dependent 
upon the voltage and certain other considerations and 
continues to rise as long as the e.m.f. is impressed. 
If it is impressed forever, the current reaches infinity; 
if for a finite time, then the oscillations have a finite 
amplitude; if at any time the exciting e.m.f. be re¬ 
moved, the oscillations continue forever at that same 
amplitude, for the circuit has no resistance. This is 











234 TEXT BOOK ON RADIO 


merely a theoretical case and cannot be attained in 
practice because of the imperfections of vacuum 
valves. Now when the negative resistance is greater 
than the positive the effective resistance of the circuit 
is negative and the free oscillations set up as the result 
of impressing an e.m.f. build up to a theoretical in¬ 
finity regardless of whether or not the external e.m.f. 
is removed. The rate of the building-up progress is 
dependent upon the amplitude of the starting e.m.f., 
which in turn depends upon the ratio of the negative 
and positive resistance and will be greater if the 
negative resistance is increased. No oscillations will 
occur until an exciting e.m.f. is impressed, but once 
that takes place, no matter how small it be, the current 
builds up to infinity. 

With this understanding of the regenerative effects 
in an audion circuit, note what Mr. Armstrong said: 

“It is, of course, impossible with present-day in¬ 
strumentalities to set up a system in which the nega¬ 
tive resistance exceeds the positive without the pro¬ 
duction of oscillations in the system, since any irregu¬ 
larity in filament emission or impulse produced by at¬ 
mospheric disturbances is sufficient to initiate an oscil¬ 
lation which builds up to the carrying capacity of the 
tube. It is, however, possible by means of various ex¬ 
pedients to set up systems which avoid the production 
of such a paralyzing oscillation and which approxi¬ 
mate the theoretical case in the use of a free oscilla¬ 
tion to produce amplification. It is the purpose of 
this paper to describe a principle of operation based 
on the free oscillation which is quantitative and with¬ 
out a loiver limit. This new method is based on the 
discovery that if a periodic variation be introduced 
in the relation between the negative and positive re- 





SUPER-REGENERATIVE SETS 


235 


sistance of a circuit containing inductance and ca¬ 
pacity, in such manner that the negative resistance is 
alternately greater and less than the positive resist¬ 
ance, but that the average value of resistance is posi¬ 
tive, then the circuit will not of itself produce oscilla¬ 
tions, but during those intervals when the negative 
resistance is greater than the positive will produce 
great amplification of an impressed e.m.f.” 

In other words, currents would increase to infinity 
and enormous amplification be possible if a non-oscil¬ 
lating circuit of negative resistance were available, 
but all such negative resistance circuits oscillate when 
excited. Mr. Armstrong accordingly sought and 
found a method whereby the effective resistance of 
ordinary regenerator may alternately be increased 
and decreased at a very rapid rate, whereby the nega¬ 
tive resistance that obtains when the negative resist¬ 
ance is greater than the positive will serve to give 
great amplification and yet in the next instant when 
the positive resistance predominates its effect shall 
be such as to prevent oscillation. In still simpler 
words, the effect is much as if he had a rapid-action 
switch which fed alternately into the circuit a nega¬ 
tive and positive resistance. 

This scheme has all the benefits of radio frequency 
amplification per se, as it is a “first power” device, 
the amplitude of the effects depending upon the am¬ 
plitude of the impressed e.m.f. Half of the time it 
is creating amplification (and the amplification when 
negative resistance predominates continues to rise 
even if the exciting e.m.f. is removed) and the other 
half of the time it is “killing oscillation.” There is 
no theoretical limit to the degree of amplification with¬ 
out oscillation—it is limited only by the carrying ca- 







236 


TEXT BOOK ON BADIO 


pacity of the tube. There is no reason why the very 
weak signal of an amateur station across the conti¬ 
nent may not be fed into a 250-watt power tube and a 
quarter kilowatt of signal-modulated output made 
available if desired. 

Now to secure this desired periodic variation in 
the ratio of the two resistances the negative may be 
varied with respect to the positive, the positive with 
respect to the negative, or both may be varied simul¬ 
taneously, any one of the methods producing the 
super-regenerative condition. The rate of variation is 
an important matter and depends upon the nature 
of the received signals. At best the choice is a 
compromise, particularly in telephony, as the lower 
the frequency the greater the amplification and the 
higher the frequency the better the quality. For tele¬ 
phony this variation frequency must be above audi¬ 
bility, and the same applies for I.C.W. and spark 
telegraphy if the natural tone is to be preserved. If 
one does not care about losing the natural note of the 
signal, then a lower frequency may be employed with 
greater amplification and a signal like receiving a 
spark on an oscillating regenerator. For C.W. teleg¬ 
raphy, where an audio note is essential, the variation 
frequency may well be 500 or 1000 cycles, but this 
note would be the same for all CAY. signals and for 
better selectivity the variation frequency may be be¬ 
yond audibility and a separate heterodyne used, 
thereby securing heterodyne selectivity and this sys¬ 
tem ’s super-amplification. 

Fig. 92 shows a practical circuit in which the nega¬ 
tive resistance is varied while the positive resistance is 
held constant. This circuit is recommended for C.W. 
and for spark, the latter presumably “on the mush.” 





SUPER-REGENERATIVE SETS 237 


Valve R, the super-regenerative amplifier, is a conven¬ 
tionally-arranged regenerator except that in its plate 
circuit is an inductance-capacity combination that is 



likewise in the plate circuit of another tube 0, the 
oscillator which creates the resistance variations. By 
O’s action the normally-generated negative resistance 





























































238 TEXT BOOK ON RADIO 


of valve R’s circuit is increased and decreased, and 
the frequency of the variation depends upon the oscil¬ 
lation constants of valve 0. Generally this is at an 
audio rate, the inductances in 0’s circuit being of the 
order of 10 to 20 henries, and of course both tubes 



Fig. 95 













































SUPER-REGENERATIVE SETS 


239 


have a big audio component in their currents. For 
this reason a third valve, a detector D, is coupled to 
the main radio-frequency inductances and the phones 
placed in its output circuit; but if a super-audible 
frequency is used in valve O the phones may be 
placed directly in the plate circuit of the amplifier 
R, and in that case, of course, sparks would be received 
on their natural note. 

Fig. 93 illustrates the variation of the positive resist¬ 
ance wfith respect to the negative, and is a circuit more 
fitted to the reception of phone. The positive resist¬ 
ance of the regenerative amplifier-detector R is varied 
by means of an oscillating tube 0, whose tuned circuit 
is completed back to filament via the inductance L 
of valve R and accordingly varies its effective resist¬ 
ance. When the grid of valve 0 is negative it has no 
effect and circuit R has normal resistance but when 
the oscillator grid becomes positive it practically 
shorts the inductance L and creates the effect of an 
excess of positive resistance therein. Although this 
circuit may employ an audio oscillator at 0, it is cus¬ 
tomary to use it at a super-audible frequency, particu¬ 
larly for telephone reception. 

Fig. 94 shows the third case in which both positive 
and negative resistances are simultaneously varied. 
For the real amateur who wants to have lots of fun 
with sixteen or so adjustments, Mr. Armstrong recom¬ 
mends this circuit. Although it is very critical of ad¬ 
justment and extreme care is necessary to obtain the 
super-regenerative state, he says it produces more am¬ 
plification than either Fig. 92 or Fig. 93. In Fig. 94 the 
amplifier R has a second feed-back circuit h 1 C 1 and L 2 
Co whereby it oscillates at some lower frequency. This 
does two things: (1) it creates a superimposed varia- 





240 


TEXT BOOK ON RADIO 


tion of the negative resistance generated in the plate 
circuit of R; and (2) at the same time it produces a 
variation in the positive resistance by varying the grid 
of valve R. The question of phase relationships be¬ 
tween the positive and negative resistances is handled 
by a variation of the coupling between Lq and L 2 , 
and by adjustment of capacities Cj. and C 2 , 
there generally being a disparity in their values. 
The separate detector D is necessary as a rectifier. 

Mr. Armstrong uses hard tubes only, rectifying on 
the lower bend by virtue of a negative grid bias and 
without condenser and leak. When the variation fre¬ 
quency is above audibility the detection may be accom¬ 
plished in the oscillating tube with still greater am¬ 
plification, as shown in Fig. 95, but the circuit is 
harder to adjust. Its action is likewise difficult to ex¬ 
plain but is somewhat as follows: incoming signals are 
amplified and become impressed upon the input circuit 
of the oscillator 0, where they are rectified by virtue 
of the grid bias battery, producing two frequencies 
in the circuit; one at signal modulation frequency and 
the other at variation frequency (O’s frequency, as 
determined by LqCj) with a super-imposed signal fre¬ 
quency component. This latter, being in tune with 
the valve 0, is amplified by its regenerative action 
and then rectified, and hence heard in the phones 

What anybody wants to cascade super-regenerators 
for we don’t know, but Air. Armstrong spoke about it. 
It seems tremendous reaction troubles are experienced 
when this is tried, but may be got around by a simple 
expedient: the second harmonic of the first amplifier 
valve is very strong, and if the input circuits of the 
second valve are tuned to this harmonic, reaction is 
avoided. Mr. Armstrong showed a diagram in which 




SUPER-REGENERATIVE SETS 


241 


the two steps of super-regeneration had their positive 
resistance varied by a single tube generator as in Fig. 
93, but with the second stage tuned to the second 
harmonic of the first stage. 

The circuit diagrams above have contemplated 
coupling the super to the antenna by means of tuned 
circuits, but Mr. Armstrong says trouble is often ex¬ 
perienced in this due to the fact that the free oscil¬ 
lations continue during the interval when the resist¬ 
ance is positive and re-excite the amplifier when the 
resistance becomes negative, with the result that the 
system oscillates. Accordingly he recommends that 
the tuning be done at one frequency and amplification 
at another, which of course is best accomplished by 
some super-heterodyne method. To accomplish this 
one would merely introduce an independent detector 
ahead of the super-amplifier and beat upon it with a 
separate heterodyne to create the amplifier frequency 
at which the super-regenerator (of whatever type) op¬ 
erates. 

This system of amplification is free of interference 
from sparks—shock excitation is eliminated. In ordi¬ 
nary spark reception what is heard is a free oscilla¬ 
tion produced by the shock of the forced oscillation 
representing the spark signal energy, but continuing 
long after the latter has ceased. 

As far as concerns the reception of long-distance 
damped and modulated signals, super-regeneration so 
far has failed to live up to expectations. By this writ¬ 
ing a great number of amateur experimenters have 
got into motion and slowly we are beginning to ac¬ 
cumulate a fund of practical data acquired in the 
hard school of experience. Almost all of these experi¬ 
menters have secured some measure of success but not 


16 








242 


TEXT BOOK ON BADIO 


of the order expected. In most cases absolutely ter¬ 
rific local signals have been obtained, and within say 
fifty miles of broadcasting stations the reception has 
been about all that could be desired; but when it 
has come to trying for long-distance 200 meter ama¬ 
teur spark telegraphy the attempts have been flat 
failures in every case which has come to our notice. 

This is a sad disappointment. Let us look into the 
matter and see if any reasons can be found for this 
failure. In the first place if there are any signals 
present from nearby stations they will be amplified— 
never fear—to such a volume that the phones can’t 
be worn for any length of time; that in itself pre¬ 
cludes much DX work; one can’t expect to fish for 
weak sparks two thousand miles , away while a half- 
horsepower of sound energy from a sink 'gap ten 
miles away is being squirted in one’s ears. Then 
again the super is full of strange noises and critical in 
its adjustments; doubtless these defects can be elimi¬ 
nated but so far they have handicapped operation. 
There is still another reason for this lack of success, 
however, and we believe it is the basic one. In his 
paper before the I.R.E. Mr. Armstrong presented 
oscillograms of the tube action. Let us quote from 
his paper: 

“....These oscillograms show phenomena which 
are in accordance with the explanations already given 
hut, in addition, show evidence of self excita¬ 
tion. It has been stated in the preceeding pages of 
this paper that the basis of super-regeneration ivas 
the discovery that a variation in the relation between 
the negative and positive resistances prevented a sys¬ 
tem which would normally oscillate violently from 
becoming self-exciting. An examination of the oscil- 





SUPER-REGENERATIVE SETS 


243 


lograms will show that this is not strictly true, as a 
free oscillation starts every time the resistance of the 
circuit becomes negative. It will be observed, how¬ 
ever, that this free oscillation is small compared to 
that produced by the signal, and therein lies the com¬ 
plete explanation of the operation of the system.” 

It seems to us that the above paragraph explains 
the trouble. Super-regeneration does not entirely pre¬ 
vent self-oscillation. As far as moderately strong 
signals are concerned, such as might be expected on a 
loop from a nearby station, the effect of these feeble 
local oscillations is entirely negligible—“and therein 
lies the complete explanation of the system.” Now 
these weak locally-excited oscillations are initiated by 
some irregularity of operation of the tubes, such as a 
miniature volcanic eruption in the filament emission, 
and the original effect is of infinitesimal order, but 
it builds up rapidly during all of the period that the 
circuit resistance is negative. Although negligible in 
the case of strong signals it seems entirely reasonable 
to consider that the amplitude of this free oscillation 
might be very formidable when compared with a 
weak signal; in which case the effect of super-re¬ 
generation wouldn’t obtain for the weak signal—in 
fact, a weak signal would actually encounter an oscil¬ 
lating tube! 

We are not trying to find theoretical fault with 
the system. It’s the other way about: the system 
has failed completely in DX spark reception and we 
are trying to find a theoretical reason w T hy. The above 
would seem to answer the question. It may be possi¬ 
ble by some innovation or even by a more skilled op¬ 
eration of the present circuits to eliminate the tend¬ 
ency toward self-oscillation but until that is done the 





244 


TEXT BOOK ON BADIO 


system does not compare, for DX damped reception, 
with an amateur short-wave regenerative circuit with 
a soft detector and two steps of audio amplification, 
even on the same loop! Amplifications of signal 
strength from 100,000 to 1,000,000 times, perhaps, but 
increase in receiving range, no! We may be wrong, 
but as we view the matter today the chief appeal of 
this particular form of super-regeneration is going to 
be for loud-speaker reception of nearby broadcasts by 
the 1 ‘ cliff-dwellers ’ ’ of big cities where it is impossible 
or undesirable to erect an outdoor aerial and where 
operation will be confined to short distances. As a 
result, the system has been dubbed “stupid-regenra- 
tion. ” 

We have been advised to use the super only on a 
loop. As a matter of fact it seems quite impossible 
on an aerial except under perfect atmospheric con¬ 
ditions. Strays and induction clicks and miscellan¬ 
eous electrical disturbances are amplified to such an 
extent that a weak signal has no chance. The set 
must be operated on a loop and sheltered as completely 
as possible from stray electrical disturbances and at¬ 
mospherics. Then if any strong signals are still 
picked up on the loop, the set will amplify them. That 
condition of course leaves very much to be desired. 

Now to get over all this gloom, we have a pleasant 
surprise. The system is delivering the goods on C.W. 
telegraph reception in a most surprising manner. We 
say surprising, because here is a system designed not 
to oscillate but to regenerate, and to super-regenerate 
and still not oscillate, a system specifically designed 
for the reception of damped and modulated signals 
and supposedly incapable of C.W. reception without a 
separate heterodyne, and here it copies ’em like a 
charm. 







SUPER-REGENERATIVE SETS 245 


Let us see if we can find an explanation for this 
unexpected C.W. reception. Frankly we don’t know 
and are only guessing. 2BML believes it possible 


























































































246 


TEXT BOOK ON RADIO 


that he is heterodyning the incoming C.W. signal 
with some harmonic of his super-audible variation 
frequency, producing beats which then of course are 
amplified in the normal super manner. 2XK, after 
slightly rearranging his circuit so that detection is 
accomplished in the first tube and after carefully 
selecting his tubes for their jobs, picks up C.W. by 
decreasing the amplitude of the variation-frequency 
energy by dimming the generator tube filament. When 
we consider that the superimposed variation fre¬ 
quency alternately increases negative resistance, per¬ 
mitting free oscillation, and positive resistance, chok¬ 



ing off the oscillations, and that normally a rather 
considerable amount of energy is required of the vari¬ 
ation generator, it seems that perhaps by dimming 
the generator filament the ratio of the negative periods 
to the positive periods would be increased to an extent 
which would permit the heterodyning of incoming 
C.W. signals without the regenerative amplifier actu¬ 
ally being in unrestricted oscillation. Still another 
possibility of accounting for C.W. reception is that 
these same feeble locally-excited oscillations which 





























SUPER-REGENERATIVE SETS 


247 


exist throughout the periods of negative resistance 
heterodyne the incoming C.W. In any event we may 
say that through some attribute of one tube or the 
other, audible beats are produced which are then re- 
generatively amplified the same as telephone signals. 

As evidence of the trend which amateur work is 
taking in the simplification of the armstrong circuits, 
consider Fig. 96, which has been used with consid¬ 
erable success. The first tube is caused to do the 
detection, and a condenser with leak is employed in¬ 



stead of the C-battery; the regeneration is controlled 
by the ordinary plate variometer instead of the de¬ 
tested tickler; and the complicated and expensive 
filter-trap across the amplifier input (necessary to 
relieve the amplifier of the heavy component of vari¬ 
ation-frequency energy) is simplified to a single large 
variable condenser across the inductance of the ampli¬ 
fier-transformer primary—it has to be tuned to the 
variation frequency, of course, but it eliminates the 
extra chokes, condensers, and resistances. The loop 






























248 


TEXT BOOK ON RADIO 


is still shown shunted across the pick-up inductance, 
an arrangement which seems to give greater stability. 
Notice variable contact X, which is decidedly to be 
recommended for control of the resistance variation 
introduced into the regenerative circuit. 

Mr. R. B. Bourne of 2BML has succeeded in adapt¬ 
ing the ubiquitous Reinartz Tuner to super-regenera¬ 
tion in the circuit shown in Fig. 97. 2BML has had 
excellent results in the reception of phones and DX 
200 meter C.W. The set worked under disadvantages, 
as a loop was used in a radio shack entirely sur¬ 
rounded by a big counterpoise. 4DL in Palm Beach, 
Fla., C.W. was heard on the loop, and an amateur 
phone somewhere in South Carolina. Spark signals 
sound “frazzled” on this hook-up unless their decre¬ 
ment is very low. In fact this circuit is at its best 
in the reception of I.C.W., particularly 500-cycles-on- 
the-plate. 8AQO paralizes the phones at 2BML, and 
1VQ, using one 5-watt tube with some form of grid 
modulation, has been heard 600 ft. from the phones 
on the equipment indicated. Of course it is possible 
that 2BML is experiencing some kind of an antenna 
effect from his counterpoise, but if that’s all that is 
necessary to make the super work we will all be will¬ 
ing to operate our loops under our aerial. 1FS, by 
the way, gets good results by hooking his antenna to 
the grid side of his loop but using no ground con¬ 
nection. 

The circuit of Fig. 98 is a one tube “flivver” cir¬ 
cuit which has been given much publicity in news¬ 
paper radio columns. Nobody knows where it started. 
Nor why a filter should be necessary. It “works,” 
as far as giving distinct evidence of the presence of 
the super effect is concerned, but it is extremely hard 






SUPER-REGENERATIVE SETS 


249 


to control the variation-frequency generation by means 
of the coupling between the two big honeycombs, and, 
in common with all the one-tube circuits on which 
we have received reports, the amplification is not sat¬ 
isfactory until the variation frequency is reduced to 
well within audibility, necessitating a separate de¬ 
tector. Then it works, but of course is no longer a 
one-tube circuit. For those interested in such cir¬ 
cuits, Fig. 99, due to P. F. Godley, is of greater pos¬ 
sibilities. The secondary S and its condenser are the 
regular closed circuit of a short-wave tuner, and the 
tickler T is the usual plate variometer but inductively 
coupled to S, for signal-frequency regeneration. The 
coupling at variation frequency is accomplished 
through the interelectrode capacity of the tube and 
controlled by condenser C, which should have a small 
choke of about 5 m.h. inductance in series with it to 
keep out the radio frequency. 

Fig. 100 is a two-tube circuit plus an extra amplifier, 
the first tube being the regenerative amplifier, the 
second acting both as oscillator and as detector, and 
the third as an ordinary audio amplifier. It is this 
set which is shown in our photograph. Note the col¬ 
lector loop, which has a dozen turns 3 ft. square. The 
vario-coupler was provided so that the plate circuit 
might be back-coupled for regeneration by means of 
the tickler, and was an ordinary Grebe coupler with 
the rotor wound with double the usual number of 
turns for the tickler. Except for the lead running 
to the input circuit of the oscillator tube 0, this first 
tube It is seen to be the familiar regenerative arrange¬ 
ment. The oscillator is tuned in both circuits to a 
super-audible frequency and to attain this has a 1250- 
turn duo-lateral coil shunted by a mica condenser of 







250 TEXT BOOK ON RADIO 


.0025 mfds. in its grid circuit, and a DL-1500 in its 
plate circuit. The two duo-laterals are not electro- 
magnetically coupled but, instead, the two circuits are 


ZOO V. 



Fig. 100 
















































SUPER-REGENERATIVE SETS 251 


statically coupled by means of the condenser C, a 
variable of .001 mfd. maximum, having in series with 
it a small inductance of 5 millihenries. This is a 
choke-coil and should be located close to the condenser 
C, which controls the amplitude of oscillations gen¬ 
erated in the valve 0. The small choke coil has little 
effect on the feed-back at the variation frequency but 
serves primarily to keep changes in the feed-back con¬ 
denser from throwing the radio frequency circuits out 
of resonance with the incoming wave. As the radio 
circuits of valve R offer considerable impedance to the 
super-audible oscillations of valve 0, a rather consid¬ 
erable power is necessary in the latter, and both R and 
O were 5-watt Western Electric power tubes with 90 
volts on their plates. 

Now if no audio-frequency amplifier is to be used, 
the phones may be connected across the fixed .005- 
mfd. condenser in the output circuit of the second 
tube. The amount of energy developed by the oscilla¬ 
tor at the variation frequency, however, is sufficient 
to completely paralyze an audio amplifier if impressed 
on its grid, and a low-pass filter is necessary between 
the detector-oscillator and the amplifier to keep out 
the 12,000-cycle component and yet pass the signal 
frequency. Any form of such filter is satisfactory, 
the arrangement shown in the diagram consisting of 
two 12,000-ohm Lavite resistances, an air variable of 
,005-mfd. maximum and an iron-cored inductance of 
0.1 henry being merely a make-shift built up of pieces 
of equipment Mr. Armstrong had at hand. The varia¬ 
ble condenser is tuned to eliminate the variation fre¬ 
quency in the amplifier by providing a shunt path 
across the primary of the amplifying transformer of 
low impedance at the frequency to which it is tuned. 





0^9 


TEXT BOOK ON RADIO 


The amplifier valve was a Western Electric telephone 
repeater with 200 volts on its plate. An additional 
200 volts is not essential; it might as well be sup¬ 
plied from an additional 110 volts and then connected 
to the same 90-volt battery that supplies the other 
tubes. 

Hard tubes were used exclusively, it being impos¬ 
sible to maintain a stable adjustment with soft tubes. 
The grid of the first tube had a negative bias of 3 
volts; this was merely to make the operation occur 
on the proper part of the characteristic curve and 
might as well have been attained by tapping off a 
different plate voltage for that tube, if any more 
convenient. 



Fig. 101 


























TO BUILD A SUPER-REGENERATIVE 

RECEIVING SET 


The parts required for a super-regenerative re¬ 
ceiver are enumerated in the legend of Fig. 102, which 
is the best of these circuits to use. 

This circuit was used very successfully with the 
super-regenerative receiver illustrated in this article. 
The constants used were as follows: 


L-l 

L-2 

C-l 

C-2 

C-3 

L-3 

L-4 

L-5 

C-4 

C-5 

C-6 

R-l 

R-2 

K-l 

C-7 

T-R 

C-8 

B-l 

B-2 

B-3 

B-4 

B-5 


Stator of vario-coupler. 

Vario-coupler with 100 turns on secondary 

.0005 m.f. variable condenser 

.001 m.f. variable condenser 

.002 m.f. fixed condenser 

D.L.-1250 

5 mil-henry inductance coil 
D.L.1500 

.001 m.f. variable condenser 
.005 m.f. fixed condenser 
.005 m.f. fixed condenser 


| 12,000 ohms non-inductive resistors 

.1 henry iron-core choke coil 
.002 m.f. fixed condenser 
Audio frequency transformer—high ratio 


.001 fixed condenser 
100 volt plate battery 
100 volt plate battery 


Variable grid batteries 
22 y >2 volt grid battery 


In the accompanying photographs one method of 
assembling this apparatus is shown. This arrange¬ 
ment was used with considerable success. It will be 

253 


254 


TEXT BOOK ON KADIO 


noted that the photographs show a variometer which 
is not indicated in the wiring diagram. This was 
used in the plate circuit of the first tube, to give a 
fine and simple control of the oscillation of this tube. 
This is not shown in the wiring diagram because, if 
the secondary of the vario-coupler is wound with 100 
turns, the variometer is not required. 

Most of the apparatus used in the super-regener¬ 
ative receiver is quite familiar and its location will 
be recognized from the photographs. 

Inquiries have been made concerning the choke coils 
and resistances in the filter circuit. These can now 
be purchased from radio dealers and it would be ad¬ 
visable to purchase the resistances. Almost any type 
of small iron-core choke coil can be used in the filter 
circuit. Final adjustments can be made by varying 
the capacities of the condenser in the filter circuit. 
The 5 mil-henry choke coil may consist of a D.L. 250 
or 300 but it can be constructed by winding 210 turns 
of No. 28 S.C.C. wire on a form 5 inches in diameter. 
The length of the coil will be about 3^4 inches. 

A suitable sized loop for the reception of 360 meters 
may be easily constructed on a frame 3-ft. square, by 
winding 7 turns of wire spaced about %-inch spart. 

Western Electric “E” tubes are the best tubes to 
employ in this circuit as the results obtained with 
“E” tubes are greatly superior to other types. 100 
volts should be used on the plate of the first two tubes 
and 200 volts on the last one. This is obtained by 
placing two 100-volt plate batteries in series with a 
center tap, as indicated in Fig. 102. 

The use of grid batteries is essential to the opera¬ 
tion of this circuit. The values of the grid voltages 
vary considerably, but are usually in the neighborhood 







SUPER-REGENERATIVE SETS 255 


of from 10 to 15 volts for each of the first two tubes 
and 22 volts for the last tube. 

A set that will give good results can be assembled 



Fig. 102 






































































256 TEXT BOOK ON RADIO 


by following diagram Fig. 103. The parts necessary 
are listed below with the same designations as shown 
in the photograph. 

Ci—0.002 mfd. fixed condenser 

C 2 —0.001 mfd. variable condenser 

C 3 —0.0005 mfd. grid condenser and 2 meg leak 

C 4 —0.0005 mfd. fixed mica condenser 

C 6 —0.001 mfd. variable condenser 

C 6 —0.002 mfd. fixed mica condenser 

Li—Single layer solenoid as described 

L 2 —200-turn honeycomb coil 

L 3 —Variometer (one with high maximum and low minimum 
values of inductance) 

L 4 —1250-turn honeycomb coil 
L 5 —1500-turn honeycomb coil 
L g —L oop antenna as described 
Rj R 2 R 3 —5-olim rheostats 
J 4 —Double-circuit jack 
J 2 —Single-circuit jack 

T—Audio-frequency amplifying transformer 
V 4 —Radiotron U.V.201 

V 2 —Moorhead or W.E. “J” tube (any hard tube will work) 
V 3 —Hard amplifier tube 

The instruments are placed on a panel as clearly 
shown in Fig. 103. 

The coil L x consists of a single layer solenoid of 
60 turns with three evenly spaced taps brought out 
to binding posts for connection to the loop for ad¬ 
justing the inductance where different sized loops 
may be used. 

The set as it was first made used a 3 volt biasing 
battery in the grid circuit of the tube V 2 , but the two 
binding posts for connecting this battery were shunted 
by a copper wire, it being found that the set worked 
just as well without any biasing batteries at all. The 
grid circuit of the tube Y 1? contains the conventional 
condenser shunted by a grid leak. This is quite an 
advantage as two batteries are thus eliminated. 





SUPER-REGENERATIVE SETS 


257 



17 


Fig. 103 























258 


TEXT BOOK ON RADIO 





Fig. 104 




















SUPER-REGENERATIVE SETS 


259 


The diagram fully illustrates the connections to the 
binding posts on the front of the panel. The binding 
posts in the diagram are arranged as looking at the 
front of the panel. The loop used was wound on a 
cross frame (30 inches across the arms) and consisted 
of fifteen turns spaced % inch between turns. Tubu¬ 
lar braided wire was used as this was found to be far 
superior to any other wire for this purpose. 

The lower left hand large knob controls the wave 
length (C 5 ), the top large knob controls the regenera¬ 
tion (L 3 ), and the right lower large knob controls the 
frequency of the tube V 2 , (oscillator). For maximum 
amplification most of the capacity of this condenser 
(C 2 ) should be included in the circuit, but for the 
clarity of telephone signals and C.W. this will have to 
be forfeited a little by reducing the capacity consider¬ 
ably. 

Of course we know that it has been generally un¬ 
derstood that the super-regenerative circuit excludes 
C.W. because the oscillator tube stops the detector 
tube from oscillating, but nevertheless if the second 
tube filament is turned down to a rather critical point, 
the amplification is retained at a near maximum, and 
C.W. signals can be received. 

The only explanation we can offer is that when the 
second tube filament is reduced in brilliancy, the am¬ 
plitude of the oscillations generated by the tube is de¬ 
creased, and their effect of stopping the detector tube 
from self oscillation at intervals is also reduced, thus 
allowing the detector to start oscillating at intervals 
between the slower frequency pulses of the second 
tube. This would produce an audio frequency beat 
when tuned properly with C.W. signals, which might 
at the same time be amplified, when its radio fre- 





260 TEXT BOOK ON RADIO 


quency component is fed back due to regeneration. 
This is only a theory, but the set actually picks up 
C.W. when in this condition very efficiently although 
with slightly different sounds than the ordinary re¬ 
generative set. 

A different adjustment is required for spark—the 
filaments must be turned up higher; sparks at best 
sound mushy but can be read without difficulty al¬ 
though the true note is somewhat distorted. 

For telephone reception the same procedure is gone 
through as for sparks, although the operator must 
make a choice between clarity of signals and degree of 
amplification. This adjustment is controlled by con- 
condenser Co; with the condenser set nearer the 0 
setting the quality will be improved and with the con¬ 
denser nearer the 100 setting on the scale, the amplifi¬ 
cation will be increased although interference from 
the oscillator frequency will be noted. 

It will be noticed that in this circuit no filter is 
used except the by-pass condenser C 6 , which is con¬ 
nected across the primary of the transformer T. This 
is all the filter necessary when using the first tube as 
the detector instead of the second tube as is ordinarily 
done. 





STORAGE BATTERIES 


The owner of a receiving set generally takes great 
care of the set itself and pays little or no attention 
to the battery. The battery must have attention if 
you desire maximum results from your set, and wish 
to save the life of your battery. 

Care of the Battery. 

In the proper care of a storage battery if the fol¬ 
lowing things are remembered you will escape 75 
per cent of your battery troubles: 

First —Test the specific gravity of all cells with a 
hydrometer two or three times a month. If any of 
the cells are below 1200, the battery is more than half 
discharged, and it should be recharged. 

Second —Pure water must be added to all cells regu¬ 
larly and at sufficiently frequent intervals to keep 
the solution at the proper height. Add water until 
solution is one-half inch above top of plates. 

Never let solution get below top of plates. 

Plugs must be removed to add water, then replaced 
and screwed on after filling. 

The battery should be inspected and filled with 
water once every week in warm weather and once 
every two weeks in cold weather. 

Do not use Acid or Electrolyte, only pure water. 

Do not use any water known to contain even small 
quantities of salts or iron of any kind. 

261 


262 


TEXT BOOK ON BADIO 


Distilled water or fresh, clean rain water only 
should be used. 

Use only a clean vessel for handling or storing 
water. 

Add water regularly, although the battery may seem 
to work all right without it. 

In order to avoid freezing of the battery, it should 
always be kept in a fully charged condition. A fully 
charged battery will not freeze in temperatures ordi¬ 
narily met. 

Electrolyte will freeze as follows: 

Sp. gr. 1,150, battery empty, 20 above zero F. 

Sp. gr. 1,180, battery % discharged, zero F. 

Sp. gr. 1,215, battery y 2 discharged, 20 below 
zero F. 

Sp. gr. 1,250 battery % discharged, 60 below 
zero F. 

Therefore, it will be seen that there is no danger of 
the battery freezing up if it is kept at a specific grav¬ 
ity of from 1250 to 1300 and it should be kept as near 
1275 as possible. Under no circumstances should acid 
or electrocute be added to the cells to bring them up 
to the required specific gravity. Nothing but pure 
water must be put in the cells after the battery has 
been once placed in commission and the specific grav¬ 
ity must be kept up by charging only. 

General Storage Battery Bata 

A storage battery, secondary battery, or accumu¬ 
lator, as it is variously called, is an electrical device 
in which chemical action is first caused by the passage 
of electric current, after which the device is capable 
of giving off electric current by means of secondary 





STORAGE BATTERIES 263 


reversed chemical action. Any voltaic couple that is 
reversible in its action is a storage battery. The 
process of storing electric energy by the passage of 


VaIv<? 


Po siKve £>ol<» 


Kle&jtiVc bole 
. .Twd rubber 
£,land cop 


Cell cover 


f-k^ptive Grid 

FVn insulator 
Side Insulator 


stsel Conti 


coll bottom 



Comber wire 
'Cell cover 
■Stuffing box, 

Qland nn^ 

Stuffing box. ^sKet 

Weld bo Cover 
Spacing washer 
■Connecting rod 
Positive ^nd 
Crid separator 
Seamless steel fir^s 

fositive tube^ 


<5v£f)erv3ion boss 


Fig. 105—Storage Cell of Nickel-Iron Type with Alkaline 

Electrolyte 


current from an external source, is called charging 
the battery; when the battery is giving off current, it 
is said to be discharging. A storage battery cell has 
two elements or plates, and an electrolyte. The two 
plates are usually made of the same material, though 
they may be of two different materials. The material 
used in the construction of both plates of battery 
furnished is lead. 



















































































































































264 TEXT BOOK ON RADIO 


Polarity .—The terms positive and negative are em¬ 
ployed to designate the direction of the flow of cur¬ 
rent to or from the battery; that is, the positive plate 
is the one from which the current flows on discharge, 
and the negative plate is the one into which current 
flows on discharge. In a lead battery the positive 
plate, on which the lead peroxide is formed, has a 
comparatively hard surface of a reddish-brown or 
chocolate color, while the negative plate, which carries 
the sponge lead, has a much softer surface of a gray¬ 
ish color. 

Electrolyte .—The electrolyte used with the lead 
type of battery is always a diluted solution of sul- 



Fig. 106—“A” Battery 


phuric acid. The specific gravity of the electrolyte 
when the battery is fully charged, varies from about 
1.210 for stationary batteries to 1.300 for automobile 
ignition batteries and other portable batteries. 





BATTERIES 265 


The proper specific gravity to use varies with the 
conditions, and the specific gravity may be found by 
the use of a hydrometer. When the cells of the bat¬ 
tery shipped with this outfit are fully charged, the 
specific gravity of the electrolyte, as indicated by 
the hydrometer, should be 1275 to 1300 at 70 degrees 
F. The final density is the usual practice. None 
but sulphur or brimstone acid should be used. When 
diluting, the acid must be poured into the water slow¬ 
ly and with great caution. 

Never Pour the Water into the Acid .—The specific 
gravity of commercial sulphuric acid is 1.835, and 1 
part of such acid should be mixed with 5 parts (by 
volume) of pure water. Care should he taken that 
no impurities enter the mixture. The vessel used for 
the mixing must be a lead-lined tank or one of w r ood 
that has never contained any other acid; a wooden 
washtub or spirits barrel answers very well. The 
electrolyte when placed in the cell should come % 
inch above the top of the plates. Before putting the 
electrolyte in the cells, the positive pole of each cell 
should be connected to the negative pole of the next 
cell in the series and the whole battery of cells 
should be connected, through a main switch, to the 
charging source—the positive pole of the battery to 
the positive side of the charging source, and the nega¬ 
tive pole of the negative side. After adding the 
electrolyte the battery should be charged at once or at 
least inside of 2 hours. A little pure water should 
be added occasionally to the electrolyte to make up 
for evaporation, and a small quantity of acid should 
be added about once a year to make up for that 
thrown off in the form of spray or that absorbed by 
the sediment in the cells. Do not use anything but 





266 


TEXT BOOK ON RADIO 


pure distilled water in storage batteries because any 
impurities such as those commonly found in tap or 
well water will in a very short time absolutely ruin 
the battery. 

Test of Specific Gravity .—The specific gravity of 
the electrolyte is the most accurate guide as to the 
state of charge of a leadtype storage battery. The 
test of the specific gravity is made by means of a 
hydrometer having a suitable scale for the type of cell 
to be tested. In all portable types of batteries, and 
ordinarily in vehicle batteries it is usually necessary 
to draw some of the electrolyte from the cell in order 
to test its specific gravity with the hydrometer, which 
should have a scale reading from 1150 to 1300. 

Charging .—The normal charging rate is the same as 
the 8-hour discharge rate specified by manufacturers. 
The charge should be continued uninterruptedly until 
complete; but if repeatedly carried beyond the full- 
charge point, unnecessary waste of energy, a waste 
of acid through spraying, a rapid accumulation of 
sediment, and a shortened life of the plates will result. 
At the end of the first charge, it is advisable to dis¬ 
charge the battery about one-half, and then immedi¬ 
ately recharge it. It is advisable to overcharge the 
batteries slightly about once a week, in order that the 
prolonged gassing may thoroughly stir up the elec¬ 
trolyte and also to correct inequalities in the volt¬ 
ages of the cells. If the discharge rate is very low, 
or if the battery is seldom used, it should be given a 
freshening charge weekly. 

Indications of a Complete Charge .—A complete 
charge should be from 12 to 15 per cent greater in 
ampere-hours than the preceding discharge. The 
principal indications of a complete charge are: (1) 





CHARGING BATTERIES 267 


The voltage reaches a maximum value of 2.4 to 2.7 
per cell, and the specific gravity of the electrolyte a 
maximum of 1275 to 1300 per cell. If all the cells 
are in good condition and the charging current is 
constant, maximum voltage and specific gravity are 
reached when there is no further increase for 14 to 
1/2 hour; (2) the amount of gas given off at the plates 
increases and the electrolyte assumes a milky ap¬ 
pearance, or is said to boil. 

Voltage Required .—The voltage at the end of a 
charge depends on the age of the plates, the tempera¬ 
ture of the electrolyte, and the rate of charging; at 
normal rate of charge and at normal temperature, 
the voltage at the end of the charge of a newly in¬ 
stalled battery will be 2 :5 volts per cell or higher; as 
the age of the battery increases, the point at which 
it will be fully charged is gradually lowered and may 
drop as low as 2.4 volts. All voltage readings are 
taken with the current flowing; readings taken with 
the battery on open circuit are of little value and are 
frequently misleading. After the completion of a 
charge and when the current is off, the voltage per 
cell will drop rapidly to 2.05 volts and remain there 
for some time while the battery is on open circuit. 
When the discharge is started, there will be a further 
drop to 2 volts, or slightly less, after which the de¬ 
crease will be slow. Cells should never be charged at 
the maximum rate except in cases of emergency. 

Direction of Current .—The charging current must 
always flow through the battery from the positive pole 
to the negative pole. If it is necessary to test the 
polarity of the line wires when no instruments are 
available, attach two wires to the mains, connect some 
resistance in series to limit the current, and dip the 





268 TEXT BOOK ON RADIO 


free ends of the wires into a glass of acidulated water, 
keeping the ends about 1 inch apart. Bubbles are 
given off most freely from the negative end. 

Discharging. —Heavy overcharging rates main¬ 
tained for a considerable time, are almost sure to 
injure the cells. The normal discharge rate should 
not be exceeded except in case of emergency. The 
amount of charge remaining available at any time 
can be determined from voltage and specific-gravity 
readings. During the greater part of a complete 
discharge, the drop in voltage is slight and very 
gradual; but near the end the falling off becomes 
much more marked. Under no circumstances should 
a battery ever be discharged below 1.7 volts per cell, 
and in ordinary service it is advisable to stop the dis¬ 
charge at 1.75 or 1.8 volts. If a reserve is to be 
kept in the battery for use in case of emergency, 
the discharge must be stopped at a correspondingly 
higher voltage. The fall in density of the electrolyte 
is in direct proportion to the ampere-hours taken out, 
and is therefore a reliable guide as to the amount 
of discharge. 

Miscellaneous Points 

Restoring Weakened Cells. —There are several 
methods of restoring cells that have become low: (1) 
Overcharge the whole battery until the low cells are 
brought up to the proper point, being careful not 
to damage other cells in the battery; (2) cut the low 
cells out of circuit during one or two discharges and 
in again during charge; (3) give the defective cells 
an individual charge. Before putting a cell that has 
been defective into service again, care should be taken 
to see that all the signs of a full charge are present. 

Sediment in Cells. —During service, small particles 





CHARGING BATTERIES 


269 


FILLER CAP AND VENT 



■SEALING COMPOUND 


STRAP 


POSITIVE 
PLATE 

PLOTTED 
RUBBER 

SEPARATOR 
WOOD 
SEPARATOR 


POST 


NEGATIVE 

PLATE 


RUBBER 

JAR 


FOOT Of 
POSITIVE 
PLATE 


FOOT OF 

NEGATIVE 

PLATE 


BRIDGES 

' 


Fig. 107—Storage Cell, Lead Plate, Acid Electrolyte Type 









270 TEXT BOOK ON EADIO 


drop from the plates and accumulate on the bottom 
of the cells. This sediment should be carefully 
watched, especially under the middle plates, where it 
accumulates most rapidly, and should never be allowed 
to touch the bottom of the plates and thus short-cir¬ 
cuit them. If there is any free space at the end of 
the cells, the sediment can be raked from under the 
plates and then scooped up with a wooden ladle or 
other non-metallic device. If this method is imprac- 





Fig. 108—Storage Battery Charging Circuit 


ticable, the electrolyte, after the battery has been fully 
charged, should be drawn off into clean containing 
vessels; the cells should then be thoroughly washed 
with water until all the sediment is removed, and the 
electrolyte should be replaced at once before the plates 
have had a chance to become dry. In addition to the 
electrolyte withdrawn, new electrolyte must be added 
to fill the space left by the removal of the sediment; 
the new electrolyte should be of 1.3 or 1.4 sp. gr. 
in order to counteract the effect of the water absorbed 
















IDLE BATTERIES 


271 


by the plates while being washed. If at any time 
any impurities, especially any metal other than lead 
or any acid other than sulphuric acid, gets into a 
cell, the electrolyte should be emptied at once and 
the cells thoroughly washed and filled with pure 
electrolyte. 

Idle Batteries .—If a battery is to be idle for, say, 
6 months or more, it is usually best to withdraw the 
electrolyte, as follows: After giving a complete 
charge, siphon or pump the electrolyte into conveni¬ 
ent receptacles, preferably carboys that have previ- 



Fig. 109—“B” Battery 


ously been cleaned and have never been used for any 
other kind of acid. As each cell is emptied, immedi¬ 
ately refill it with water; when all the cells are filled, 
begin discharging and continue until the voltage falls 
to & or below 1 volt per cell at normal load, and then 
draw off the water. 

Putting Battery into Commission .—To put an idle 
battery into commission, first make sure that the con¬ 
nections are right for charging; then remove the 
water, put in the electrolyte, and begin charging at 
once at the normal rate. From 25 to 30 hours con- 







272 TEXT BOOK ON BADIO 


tinuous charging will be required to give a complete 
charge. 

Sulphating .—Lead sulphate is practically an in¬ 
sulator. Some of this material is formed in all lead- 
sulphuric-acid storage cells on discharge and is re¬ 
converted to lead oxide or lead peroxide on recharg¬ 
ing the cell. If present in excessive quantities, the 
sulphate adheres to the plates, especially the positive, 
in white soluble patches, preventing chemical action, 
increasing the resistance of the cell, and causing un¬ 
equal mechanical stresses that may buckle the plates. 
The most frequent causes of sulphating are overdis¬ 
charging, too high specific gravity of electrolyte, and 
allowing the battery to stand for a considerable length 
of time in a discharged condition. 





GENERATOR TROUBLES, THEIR CAUSES 

AND REMEDY 


Methods for Locating and Repairing Break in the 

Armature of Generator. 

A break in an armature must be located by the fall 
of potential method, which means that a current must 
be sent through the armature and the voltage tested 
across the various segments. First disconnect all the 
leads from the armature and lift all brushes except 
one on each pole, then connect the battery to these 
brushes through the resistance and ammeter shown 
in Fig. Ill, connect the detector to one brush, and 
then to each segment in turn with a wire from the 
other terminal of detector until the break is located. 

If the two wires from the detector are connected to 
the segments that the brushes are standing on, a de¬ 
flection will be seen caused by a fall of voltage through 
the coils. If we gradually draw the movable wire 
over the segments toward the other brush, the deflec¬ 
tion will gradually fall to zero, providing it is on the 
side on which the break does not occur (Fig. 111). If 
however, the wire is drawn over the segments on the 
other side, the deflection on the instrument will re¬ 
main constant until the failing segment is reached, 
when the deflection will drop to zero as the wire 
passes over the break. 

Instead of moving the testing wire around the com¬ 
mutator, a course that might not always be conveni¬ 
ent, it could be held stationary against the commu¬ 
tator, say a few segments from one of the brushes, 

273 


18 


274 TEXT BOOK ON EADIO 


and the armature gradually pulled around till the 
break appeared. 

In this case on the unbroken side a constant deflec¬ 
tion will be obtained till the break passes a brush, 
when the needle will fall to zero. On the other side 
there will be no deflection till the break passes one 
of the brushes. So long as the break is between the 
movable testing wire and the brushes to which the 


\ 



Rotation 


[Fig. 110—Correct Method of Setting Brushes 











GENERATORS 


275 


detector is connected, there is a deflection; but not 
when the break is between the fire brushes and the 
testing wire. If the instrument gives a good reading 
between two adjoining segments, it will show a much 
larger reading across a break. 

If a millivoltmeter is available, the matter is some¬ 
what simplified, as a small current is sufficient for 
testing, such for instance as the current taken by an 
incandescent lamp. If, therefore, the armature be 
connected to a source of supply through a lamp, a 
millivoltmeter vfill give a good deflection across a 
break. Millivoltmeter is the instrument used as a 
shunted ammeter in conjunction with various law re¬ 
sistances called shunts; when used as a millivoltmeter 
in the manner above described, it is used alone, the 
armature itself taking the place of the shunt (Fig. 
112 ). 

Having found the broken section it must be exam¬ 
ined till the actual break is discovered. In the case 
of a winding, the bad section can be taken out and 
a new one put in without much difficulty. In the case 
of a formed wound drum, it is generally an inacess- 
able bottom wire that breaks. In this case it is usual 
to strip the armature till the break is reached; this 
is not always necessary. Having found the defective 
section, cut out as much as can be got at, that is the 
conductors on the surface of the core or in the slots. 
Leave the end crossing wires in, but with the ends 
separated and rewind the section with the end cross¬ 
ings on top of the others. 

Overheating of the Armature 

Several causes will cause overheating of the arma¬ 
ture, the most common being—overload, grounds, 
eddy currents in the core, eddy currents in the con- 





276 


TEXT BOOK ON RADIO 


ductors, short-circuit in the coils, sparking at the com¬ 
mutator, heat conducted from the bearings, low insula¬ 
tion. If the excessive heating is uniform over the 
whole armature, the machine is overloaded. 

Should one or two of the coils be overheated, the 
trouble is due to a short circuit in the winding. If 
the core is hotter than the coils, the trouble is due 
to excessive eddy currents in the laminations, caused 
by the core rubbing up against one of the pole faces, 
or it may be caused by a number of the laminations 
being short-circuited, the slots having been filed too 
much when the core was built. Heating due to eddy 
currents either in the armature core or the conductors, 
cannot be remedied by the projectionist, the maker of 
the machine should be immediately notified. The test 
is to run the generator on open circuit and take note 
of the rise in temperature. To test for a ground in 
the windings, first disconnect the generator from the 
circuit, and then run it up to normal speed. Using 
an ordinary test lamp, touch the opposite brushes 
to make sure you have the voltage. 

Then connect the lamp terminals between the gen¬ 
erator frame and the poles. Should there be a 
ground the test lamp will either glow or light. The 
cause of the ground should then be located and re¬ 
moved. 

Locating Grounded Coil 

To locate a grounded coil is a difficult job, and 
should not be undertaken by anyone who is not fa¬ 
miliar with electrical apparatus. 

The armature should be removed from the field 
and set on trestle, a current (not to exceed the normal 
current of the dynamo) should be passed through the 
armature from any one of the commutator segments 






GROUNDED COIL 


277 


to the shaft. A compass should be held near the con¬ 
ductors, and the needle will be deflected in a certain 
direction due to the flow of current. If the armature 
is slowly turned round, till such time as the compass 
needle reverses, this will indicate the proximity of the 
grounded coil. 

Low insulance (insulation resistance) between the 
core and the armature winding, is generally caused by 
the presence of moisture, and often accompanied by 
vapor arising from the armature. This can be reme- 

7WS, 



died by baking the armature in an oven at a tempera¬ 
ture of about 200° F, or by running the machine un¬ 
loaded for a few hours and sending a small current 
round the windings. 

The short circuiting of the coils is generally accom¬ 
panied by heavy sparking and a smell of burning may 
be caused by copper dust, oil on bits of solder lodged 
between the commutator arms. 











278 


TEXT BOOK ON BADIO 


Locating Short-Circuited Coil 

To locate a short-circuited coil, use the same method 
to locate break in armature. It is best to test between 
each pair of segments, remembering that the readings 
will all be alike when connected across the good coils, 
and that a variation in the reading points to a fault. 

The remedy for a short circuited coil is to strip the 
damaged parts and rewind. 

A temporary repair job can be accomplished by 
disconnecting the short circuited coil from the com¬ 
mutator arms, and then bridging the arms, thus cut¬ 
ting out the defective coil. 

Should the short circuiting of the coils be due to 
copper dust, oil, etc., between the commutator arms, 
all that will be necessary will be to dislodge the foreign 
substance. 


Overheated Bearings 

A hot bearing may result from one or more of 
the following causes: Insufficient lubrication, faulty 
lubrication, grit or other foreign matter in the bear¬ 
ings ; armature not centered with respect to pole 
pieces; side pull due to magnetic pull on armature; 
end pressure of collar against the bearing—due to 
machine being out of line, with its driving shaft, or to 
want of alignment in engine; to a bent armature 
shaft; shaft rough or cut, etc., etc. 

Only the best of oil, free from sediment and grit 
should be used for lubrication (the ordinary machine 
oil supplied and used on the projector is too thin for 
this class of work) all the oil cups should be kept 
clean and filled, the oil rings should be watched to 
see that they carry the oil up to the shaft. 

When the heating of a bearing is due to the pres- 





OVERHEATED BEARINGS 


279 


ence of dirt or grit, it should be cleaned with some 
thin oil or kerosene. If kerosene is used do not forget 
to use a good lubricant directly after the cleansing. 

The bearing caps should just be tight enough to run 
freely, without any side play. If a bearing is too 
tight the oil cannot get through as the oil passage re¬ 
mains full. The same thing occurs if the oil passages 
become choked with dirt or grit. 

Do not tighten up the bearing caps with pliers, as 
sufficient pressure can be brought to bear with the 
finger and thumb. After tightening up the caps the 
armature should revolve freely, and when in motion 
the armature should come gradually to rest. Should 
the armature stop quickly the bearings are too tight. 

A bent shaft will cause the armature to rub pole 



lamp 


Fig. 112 


pieces, and thus produce sparking, vibrations and 
overheating. To overcome this it will be necessary to 
remove the armature from the machine and have the 
shaft straightened in what manner is most handy. It 
may be found necessary to withdraw the shaft from 
armature before this can be accomplished. 

A rough shaft may be caused by dirt, grit or over- 








280 TEXT BOOK ON RADIO 


heating. The roughness, if not excessive, can be taken 
out by the use of a little emery cloth, but care should 
be taken to remove all grit and filings when the job 
is finished. If the roughness is so great that it cannot 
be taken out with the use of emery cloth, it will be 
necessary to remove the armature, and smooth up the 
shaft in a lathe, using a very fine file and emery 
cloth. 

Noise in a generator can be laid to one of the fol¬ 
lowing causes: Bent or broken shaft; armature out 
of balance; brushes grinding commutator; armature 
hitting pole pieces; loose bearings. All screws and 
bolts should be periodically gone over and any loose 
one tightened. If the noise is due to the armature 
not being properly balanced, the makers of the ma¬ 
chine should be notified, as this is due to faulty con¬ 
traction of the generator. 

A grinding or squeaking noise from the brushes 
can sometimes be stopped by the application of a very 
little vaseline to the commutator. If, however, the 
noise continues, the brushes should be removed and 
examined to see that a “hard place’’ has not de¬ 
veloped. Should this be the case, the brushes should 
be filed down past the “hard place” and then re¬ 
placed in the holders. 

In the event of a short-circuit a fuse would nat¬ 
urally blow, and all generators should be fused up as 
near the terminals as possible. 

A series-wound generator would spark and pull 
the engine up. It would not give any current to the 
arc. 

A compound-wound generator would spark and 
show a drop in voltage. 

A shunt-wound generator would lose its field and 





GENERATORS 


281 


would not excite till such time as the short was re¬ 
moved. 

When a generator is overloaded, the temperature 
of the armature will rise, and heavy sparking of the 
brushes will also result. If the machine is run with¬ 
out removing the overload, the insulation of the arma¬ 
ture may be destroyed. 



Fig. 113 










MOTOR TROUBLES AND REMEDIES 


Sparking may be due to overload, wrong position of 
brushes, broken coil, weak field, and to any of the 
causes named for dynamos. 

Sparking 

Symptom. Intermittent Sparking. On a varying 
load, in which the work comes on at the beginning 
or end of each cycle, and then falls off during the 
remainder of the cycle, a motor often sparks just as 
the peak load comes on. 

The cause is the heavy current taken at the instant 
of maximum load, which distorts and weakens the 
effective field and shifts the neutral point. This 
weakening of the field results in a still larger current 
in the armature, aggravating the evil. 

Remedy. Add a compounding coil on the motor to 
assist the shunt, or exchange the motor for a com¬ 
pound-wound one, or one with interpoles. 

Failure to Start 

(1) Symptoms. Motor does not start. Little or no 
current passes on closing the D.P. switch and pushing 
starting handle over. 

Probable Causes. Brushes not down. Switch not 
making contact in the jaws. Starting switch not 
touching the contacts. Fuse broken. Controller fingers 
not touching contact plates. Break in series coil (if a 
series motor). Terminal loose. No current on mains. 


282 


MOTOR TROUBLES 283 


If the no-volt release coil excites, or if a long arc 
is observed on breaking circuit, it indicates that the 
shunt field gets its current and the probable cause of 
the failure to start is that the shunt is connected in 
series with the armature owing to two of the leads 
from the starter being reversed. 

Remedy. Trace out the connections or use testing 
set. 

Failure to Start 

(2) Symptom. Motor does not start, but takes ex¬ 
cessive current. Fuse or overload cut-out acts. 

Cause. It is assumed the motor is not overloaded; 
this can be tested by taking load off and trying to 
start motor light. If a shunt motor there may be a 
short circuit in connecting cables or in field coil; or 
in armature; or a break in field coil. 

Remedy for broken field. If field excites when 
brushes are up, but not when they are down, the 
symptoms point to a short circuit in or across arma¬ 
ture, or brushes. 

Examine brushes for short circuit to frame, for 
copper dust, oil, or broken down insulation. 

Then disconnect armature and excite field. Move 
armature round quickly by hand. A drag will be 
felt as the short circuited coils pass the holes. If the 
armature can be driven at a fair speed by belt, with 
the field excited, the short-circuited coils will warm 
up and can probably be located in this way. 

If the above symptoms occur with a series-wound 
motor, the cause may be a short in the field or arma¬ 
ture, but not a break. 

A fairly common cause is incorrect connecting up. 

Another cause , particularly with machines that have 





284 TEXT BOOK ON RADIO 


been dismantled, is incorrect polarity of the field coils. 
Thus if the coils are connected up so that they are all 
of the same polarity, the effect is the same as with a 
broken field wire as the field is completely neutralized. 
If only one of the field coils is reversed in a four-pole 
motor, the motor would probably not start and would 
in any case take an excessive current. 

Remedy. Test the coils for polarity. 

Incorrect Speed 

A certain amount of speed adjustment may be ob¬ 
tained by altering the position of the brushes. Moving 
the brushes backwards from the neutral point has the 
effect of increasing the speed, whilst moving them 
forward reduces the speed. 

Excessive Speed 

Symptom. Motor starts, then speed gradually in¬ 
creases till motor runs at very excessive speed. This 
only occurs when a motor starts light or on a very 
light load such as a loose pulley. 

Cause. If shunt or compound motor. Shunt coil 
connected in series with armature instead of in 
parallel. 

On first switching on, the magnets excite, as the 
armature is stationary and allows the full shunt cur¬ 
rent to pass the coils. As the armature speeds up it 
puts a back emf in the circuit, gradually reducing 
the current passing and thus weakening the field. 
The faster the armature goes the weaker the field 
becomes. A short circuit in the shunt might pro¬ 
duce same result if motor starts absolutely light. 

Remedy. Connect up the shunt. 





MOTOR TROUBLES 


285 


Fuse Blows 

Symptom. Motor starts and runs np to its proper 
speed, but fuse or overload acts on putting load on. 

Cause. This is a sign of overload. Probably belts 
too tight, bearings tight or dry. 

If the fuse blows while starting up there may be 
be h ground on the motor. This should be tested. If 
the starter is provided with shunt sector the fuse may 
blow while starting up, owing to a bad contact to 
this sector, due either to dirt or to a hollow place in 
the metal. 

In the case of a compound-wound motor a cross 
connection or leakage between the series and shunt 
windings will cause the fuse to blow if the cross is 
in a position that the shunt is practically short cir¬ 
cuited bv the series. 

«/ 

Starter Overheats 

Symptom. Motor starting against load takes exces¬ 
sive current. Last few coils of resistance overheat 
(probably smoke or get red hot). Fuse or overload 
acts, or motor sparks. 

Cause. Overload; or starter too small. 

When a motor starts against a load having consid¬ 
erable inertia, such as heavy line shaft with several 
large pulleys and tight belts, or against a heavily fly¬ 
wheeled machine, time must be given for it to get 
up speed. If the starter is moved over the contacts 
more quickly than the motor can accelerate, an ex¬ 
cessive current will pass, causing the motor to spark. 
The starter must be put on more slowly and this will 
cause it to heat up unless it has been liberally rated. 

Remedy. Exchange starter for one having more 





286 TEXT BOOK ON EADIO 


margin, that is one which permits of starting up 
slower. This does not mean a starter for a large H.P. 

Starts Suddenly 

Symptom. Motor does not start nor take current 
till most of resistance is cut out, then takes rush of 
current and starts suddenly. 

Cause. —A break in the starting resistance. Tempo¬ 
rary Remedy. Connect the contacts where breaks oc¬ 
curs, until resistance can be repaired. 

Wrong Direction 

Symptom. Motor runs in wrong direction. 

Remedy. Reverse armature or field connections, 
whichever is easier, but not both. 

In a compound-wound machine both the shunt and 
series coil must be reversed if the field be reversed; 
but if the machine be provided with interpoles these 
must be treated as part of the armature and must 
therefore not be reversed when the field is reversed. 

More Reverses 

Symptom. Motor starts up and runs correctly on 
light load. On an overload, or reduced voltage, motor 
reverses and runs backwards. 

Cause. This applies to a compound-wound motor, 
with the series or compound coil connected up in op¬ 
position to the shunt coil. 

Remedy. Reverse the series coil. 

Flashing 

Symptom. Severe sparking or flashings apparently 
all round the commutator; overheating of the arma¬ 
ture and burning of the insulation between a couple 
of the segments. 





MOTOR TROUBLES 


287 


Cause. The cause of the above is a broken wire in 
the armature winding. 

Remedy. If the broken end cannot be located and 
repaired easily, the armature must be stripped until 
the break is found and the section re-wound. A 
temporary repair can sometimes be made sufficiently 
to enable the motor to continue working, by joining 
across the two segments on each side of the burnt 
mica with a short piece of copper wire, the wire being 
laid on the ears of the commutator and sweated in with 
a soldering iron. This practically converts two seg¬ 
ments into one, and the motor will run in this way 
quite satisfactorily. If the commutator lugs are not 
readily accessible, a copper pin may be driven hard 
down between the two segments in a part not under 
the brushes. 


Flashing Over 

Symptom. On an overload and sometimes on a 
normal load a motor will flash from the brushes to 
a part of the commutator or to the rocker, and blow 
the fuses. This is more liable to happen with a 
weak field. 

Cause and Remedy. The cause is that the motor 
has too much forward lead, and the brushes should 
be moved back a little. 





REGULATIONS FOR THE INSTALLATION 

OF AERIALS 


a. Antennae outside of buildings shall not cross 
over or under electric light or power wires of any 
circuit carrying current of more than 600 volts, or 
railway trolley or feeder wires, nor shall it be so 
located that a failure of either antenna or of the 
above mentioned electric light or power wires can re¬ 
sult in a contact between the antenna and such electric 
light or power wires. 

Antennae shall be constructed and installed in a 
strong and durable manner and shall be so located 
as to prevent accidental contact with light and power 
wires by sagging or swinging. 

Splices and joints in the antenna span, unless made 
with approved clamps or splicing devices, shall be 
soldered. 

Antennae installed inside of buildings are not cov¬ 
ered by the above specifications. 

b. Lead-in wires shall be of copper, approved 
copper-clad steel or other approved metal which will 
not corrode excessively, and in no case shall they be 
smaller than No. 14 B. & S. gauge except that ap¬ 
proved copper-clad steel not less than No. 17 B. & S. 
gauge may be used. 

Lead-in wires on the outside of buildings shall not 
come nearer than four (4) inches to electric light 
and power wires unless separated therefrom by a con¬ 
tinuous and firmly fixed non-conductor that will main- 


288 


AERIAL INSTALLATION 289 


tain permanent separation. The non-conductor shall 
be in addition to any insulation on the wire. 

Lead-in wires shall enter building through a non¬ 
combustible, non-absorptive insulating bushing. 

c. Each lead-in wire shall be provided with an 
approved protective device properly connected and 
located (inside or outside the building) as near as 
practicable to the point w T here the wire enters the 
building. The protector shall not be placed in the 
immediate vicinity of easily ignitible stuff, or where 
exposed to inflammable gases or dust or flyings of 
combustible materials. 

The protective device shall be an approved lightning 
arrestor which will operate at a potential of 500 volts 
or less. 

The use of an antenna grounding switch is desirable 
but does not obviate the necessity for the approved 
protective device required in this section. The an¬ 
tenna grounding switch, if installed, shall, in its closed 
position, form a shunt around the protective device. 

d. The ground wire may be bare or insulated and 
shall be of copper or approved copper-clad steel. If 
of copper, the ground wire shall be not smaller than 
No. 14 B. & S. gauge, and if approved copper-clad 
steel, it shall be not smaller than No. 17 B. & S. 
gauge. The ground wire shall be run in as straight 
a line as possible to a good permanent ground. Pref¬ 
erence shall be given to water piping. Gas piping 
shall not be used for grounding protective devices. 
Other permissible grounds are grounded steel frames 
of buildings or other grounded metallic work in the 
building and artificial grounds such as driven pipes, 
plates, cones, etc. 

The ground wire shall be protected against me- 

19 





290 TEXT BOOK ON BADIO 


chanical injury. An approved ground clamp shall be 
used wherever the ground wire is connected to pipes 
or piping. 

e. Wires inside buildings shall be securely fastened 
in a workmanlike manner and shall not come nearer 
than two (2) inches to any electric light or power 
wire unless separated therefrom by some continuous 
and firmly fixed non-conductor making a permanent 
separation. This non-conductor shall be in addition 
to any regular insulation on the wire. Porcelain 
tubing may be used for encasing wires to comply with 
this rule. 

f. The ground conductor may be run inside or 
outside of building. When receiving equipment 
ground wire is run in full compliance with rules for 
Protective Ground Wire, in Section d., it may be used 
as the ground conductor for the protective device. 








REQUIREMENTS OF NATIONAL ELEC¬ 
TRICAL CODE-RADIO INSTALLATION 


Where an indoor aerial is used, no special safe¬ 
guards are necessary, but where the aerial is placed 
outside the building, a ground wire should be carried 
from the aerial in the most direct line to the ground. 
This wire should not be smaller than No. 8 B. & S. 
gauge. Should it not be possible to make a suitable 
ground connection outside the building, then the 
ground wire should be lead into the cellar of build¬ 
ing through a lead-in insulator and connection made 
to the water main. Do not under any circumstances 
connect the ground wire to a gas pipe. The lead-in 
wire from the aerial to the receiving set should be 
protected by one of the approved types of lightning 
arrestors now on the market. This arrestor should be 
installed on the lead-in wire outside the building. 

A. Aerial conductors must be installed and con¬ 
structed to prevent accidental contact with the con¬ 
ductors carrying a current over 600 volts. Aerial 
supports must be constructed and installed in a strong 
and durable manner. Aerial wires leading from same 
to ground switch must be mounted firmly on approved 
insulating supports which may be constructed of 
wood, not iron pin, or brackets equipped with porce¬ 
lain knobs or petticoat insulators. Insulators must 
be so installed as to maintain the conductors at least 
five inches clear of the surface of the building wall. 
In passing the aerial conductor through the side of 
the building a continuous tube or bushing must ex- 

291 


292 


TEXT BOOK ON BADIO 


tend five inches beyond the surface of the walls on 
both sides. The porcelain tube will not be approved 
in this case. Ground switches shall be mounted so 
that the current carrying parts will be at least five 
inches clear of the building walls and located prefer¬ 
ably in the most direct line between the aerial and 
the point of ground connection. The conductor from 
the ground switch to ground connection must be se¬ 
curely supported. 


B. Aerial conductors must be effectively and per¬ 
manently grounded at all times when the station is 
not in operation, by a conductor the periphery of the 
cross section of which is not less than three-quarters 
of an inch. The ground conductor must be of copper 
or other metal which will not corrode excessively 
under existing conditions. Where ground conductor 
is over twenty-five feet in length it shall be insulated 
throughout its entire length in a similar manner to 
wires attached to aerial conductors. Ground connec¬ 
tions should be made in accordance with the require¬ 
ments as set forth above, except where variations from 
these requirements may be allowed by special permis¬ 
sion in writing from the Board of Fire Underwriters. 


C. In radio stations used for receiving only the 
ground switch may be replaced by a similarly mounted 
and grounded short (one-eighth inch or less) or 
vacuum type lightning arrestor. The current carry¬ 
ing parts must be five inches from the building. 


D. Where the aerial is grounded as specified in 
sections A and B the switch employed to join the 
aerial to the ground connection must be a knife 










NATIONAL CODE—RADIO INSTALLATION 293 


switch, the blade of which must have a periphery of 
less than three-quarters of an inch so that when open 
the current carrying parts to which the aerial and 
ground connection wires are attached will be sep¬ 
arated at least by five inches. The base of the switch 
must be of a material suitable for high frequency 
service. Slate will not be approved. 

E. When supply is obtained direct from street 
service the current must be installed in metal con¬ 
duit or armored cable. In order to protect the supply 
system from high potential surges there must be pro¬ 
vided two condensers, each of not less than one-half 
microfarad capacity and capable of withstanding 
600-volt tests in series across the line with mid-point 
grounded. A capacity fuse not larger than ten am¬ 
peres capacity must be connected between each con¬ 
denser and the line wire connected to it. Each 
condenser must be protected by a shunting fixed spark 
gap of one thirty-second of an inch separation or 
less. Another way of protecting the supply system 
from high potential surges is by means of two in¬ 
candescent lamps connected in series across the line 
with the mid-point grounded. 

F. Transformer, voltage reducers, keys and similar 
devices must be of types specially designed for the 
service. 






U. S. RADIO LAWS AND REGULATIONS 


The owner of an amateur radio transmitting station 
must obtain a station license before it can be operated 
if the signals radiated therefrom can be heard in an¬ 
other state; and also if such a station is of sufficient 
power as to cause interference with neighboring li¬ 
censed stations in the receipt of signals from trans¬ 
mitting stations outside the state. These regulations 
cover the operation of radio-telephone stations as well 
as radio-telegraph stations. 

Station licenses can be issued only to citizens of 
the United States, its territories and dependencies. 

Transmitting stations must be operated under the 
supervision of a person holding an Operator’s Li¬ 
cense and the party in wdiose name the station is 
licensed is responsible for its activities. 

The Government licenses granted for amateur sta¬ 
tions are divided into three classes as follows: 

Special Amateur Stations known as the “Z” class 
of stations are usually permitted to transmit on wave 
lengths up to approximately 375 meters. 

General Amateur Stations which are permitted to 
use a power input of 1 kilowatt and "which cannot 
use a wave length in excess of 200 meters. 

Restricted Amateur Stations are those located 
within five nautical miles of Naval radio stations, and 
are restricted to % kilowatt input. These stations 
also cannot transmit on wave lengths in excess of 200 
meters. 


294 


U. S. KADIO LAWS 295 


Experimental stations, known as the “X” class, 
and school and university radio stations, known as 
the “Y” class, are usually allowed greater power 
and also allowed the use of longer wave lengths at 
the discretion of the Department of Commerce. 

All stations are required to use the minimum 
amount of power necessary to carry on successful com¬ 
munication. This means that while an amateur sta¬ 
tion is permitted to use, when the circumstances re¬ 
quire, an input of 1 kilowatt, this input should be 
reduced or other means provided for lowering the 
antenna energy when communicating with near-by 
stations in which case full power is not required. 

Malicious or wilful interference on the part of any 
radio station, or the transmission of any false or 
fraudulent distress signal or call is prohibited. Se¬ 
vere penalties are provided for violation of these pro¬ 
visions. 

Special amateur stations may be licensed at the 
discretion of the Secretary of Commerce to use a 
longer wave length and higher power than general 
amateur stations. Applicants for special amateur 
station licenses must have had two years’ experience 
in actual radio communication. A special license will 
then be granted by the Secretary of Commerce only 
if some substantial benefit to the science of radio 
communication or to commerce seems probable. Special 
amateur station licenses are not issued where indi¬ 
vidual amusement is the chief reason for which the 
application is made. Special amateur stations located 
on or near the sea coast must be operated by a person 
holding a commercial license. Amateur station li¬ 
censes are issued to clubs if they are incorporated, 
or if any member holding an amateur operator’s li- 





296 


TEXT BOOK ON RADIO 


cense will accept the responsibility for the operation 
of the apparatus. 

Applications for operator’s and station licenses of 
all classes should be addressed to the Radio Inspector 
of the district in which the applicant or station is 
located. Radio Inspectors’ offices are located at the 
following places. 


First District. . , 
Second District 
Third District. . 
Fourth District. 
Fifth District. .. 
Sixth District. . . 
Seventh District 
Eighth District. 
Ninth District. . 


.Boston, Mass. 

. .. .New York City 
. ... Baltimore, Md. 

.Norfolk, Va. 

. .New Orleans, La. 
San Francisco, Cal. 
....Seattle, Wash. 

.Detroit, Mich. 

.Chicago, Ill. 


No license is required for the operation of a receiv¬ 
ing station, hut all persons are required by law to 
maintain secrecy in regard to any messages which may 


be overheard. 


There is no fee or charge for either an operator’s 
license or a station license. 













A GLOSSARY OF RADIO WORDS AND 
THEIR DEFINITIONS 


A. C. ALTERNATING CURRENT. A current that changes 
its flow of direction a given number of times a second, 
according to the construction of the alternator. 

ACCELERATION. Rate of change of velocity. 

ACCUMULATOR. A storage battery. 

ACLINIC LINE. The line that represents the magnetic 
equator. 

ACOUSTICS. The science of sound. 

ACTINIC RAYS. The rays at the violet end of the spectrum. 

ACTINOMETER. A photometer; a meter for measuring the 
sun’s rays. 

ACTUAL HORSEPOWER. The exact useful power given 
out by a machine; found by subtracting the power used 
by the machine itself from the indicated horsepower. 

ADAMANT. A substance of extreme hardness such as the 
diamond. 

ADJUSTABLE CONDENSER. A condenser, any part of 
which may be cut in or out of the circuit; thus varying its 
capacity. 

ADMITTANCE. One ohm has an admittance of one mho; the 
reciprocal of impedence. 

AERIAL. A system of wires used to radiate or receive energy 
in the form of electro-magnetic waves. The wires should 
be strung clear of, and insulated from all surrounding 
objects. 

AEROMETER. A meter for measuring the tension of the 
air. 

ALIGN. To place or form in line. 

ALLOY. A mixture of two or more metals. 

ALTERNATOR. An alternating current dynamo. 

ALTERNATING CURRENT. See A. C. 

ALUMINUM. A light malleable white metal. Specific Grav¬ 
ity 2.6. (A conductor of electricity.) 

AMALGAM. An alloy, part mercury. 

AMMETER. An instrument used to measure the flow of cur¬ 
rent, and connected in series in the circuit. 

AMPERE. The unit of current strength. 

297 


298 TEXT BOOK ON RADIO 


AMPERE HOUR. The quantity of electricity passed by a 
current of one ampere in one hour; 

One ampere flowing for one hour; 

Two amperes flowing for one-half hour; 

One-half ampere flowing for two hours, all equal one am¬ 
pere hour. 

AMPLIFIER. An instrument to increase the volume of a 
receiving signal. There are a number of different types 
on the market such as vacuum-tube, magnetic, etc. 

ANCHOR BOLTS. Bolts used to fasten machines to their 
foundation. 

ANCHOR GAP. A spark gap used to disconnect the detector 
when using the transmitter. 

ANEMOMETER. A meter for measuring the direction and 
velocity of the wind. 

ANEROID BAROMETER. An instrument for measuring at¬ 
mospheric pressure. 

ANGLE OF DECLINATION. Variation of a compass; the 
angle of error of the magnetic compass. 

ANGULAR VELOCITY. The speed of a revolving or turning 
body. 

ANNULAR. Having the form of a ring; ring shaped. 

ANODE. Positive terminal of a conducting current. 

ANTENNA. A receiving aerial. 

ANTI-FRICTION METAL. A tin, lead alloy like Babbitt 
Metal. 

ANTI-INDUCTION CONDUCTOR. A conductor so made that 
it avoids induction effects. 

ANTI-SPARK DISCS. Discs made of Ebonite used to assist 
in preventing sparking on Bradfield tube. 

APERIODIC. Not tuned. 

APERTURE. An opening of any description in a partition. 

ARC. The arc between the two carbon electrodes slightly 
separated. 

ARC RECTIFIER. An apparatus used to change Alternating 
Current to Direct Current. 

AREOMETER. An instrument for finding the specific gravity 
of a fluid. 

ARMATURE. A collection of pieces of iron designed to be 
acted on by a magnet ; a part of a generator. 

ARMATURE BORE. The space within which the armature 
revolves. 

ARMATURE COILS. The wires wound on the core of the 
armature. 

ARMOR CABLE. Wire enclosed in a metal protective cover¬ 
ing. 





RADIO TERMS 


299 


ARTIFICIAL MAGNET. A piece of iron or steel that has 
been magnetized. 

ASBESTOS. A fibrous variety of ferro-magnesium silicate. A 
non-conductor of heat, and fireproof. 

ASBESTOS COVERED WIRE. A cable of very fine strands 
of copper wire all twisted together and covered with an 
asbestos covering. 

ATMOSPHERE. Air, a mixture of gases. 

ATOM. The smallest division of a substance. 

ATTENUATE. To make thin; to lessen the force of. 

AUDION. A relay operated by electrostatic control of cur¬ 
rents flowing across a gaseous medium; consists of a heated 
filament, a grid electrode and a metal plate all enclosed in 
a highly evacuated bulb. 

AUDIOMETER. A meter for measuring the strength of in¬ 
coming signals. 

AURORA BOREALIS. A luminous display and electrical 
phenomenon seen in the heaven in the northern hemisphere. 

AUTOMATIC. Self-acting. 

AUTOMATIC TRANSMITTER. A transmitter operated by 
running a paper tape between small metal wheels. 

AUTOMATIC TRANSFORMER. A transformer provided 
with one coil instead of two, part of the coil being tra¬ 
versed by the primary and part by the secondary current. 

AUXILIARY ANODE. The third element of the amplifier. 

A. W. G. American Wire Gauge. 

B. A. British Association. 

B. and S. W. G. Brown and Sharpe Wire Gauge. 

B. W. G. Birmingham Wire Gauge. 

B. X. Metal tubing containing twin conductors each insulated 
from the other and both wires wrapped so as to completely 
fill the tubing. 

BABBITT METAL. An anti-friction metal. 

BALANCE, ELECTRIC. Wheatstone bridge. 

BALANCING SET. A dynamo used in a three wire system 
to balance the electromotive force. 

BALANCE WHEEL. A fly wheel; a wheel added to machines 
to prevent too sudden variations in speed. 

BALL AND SOCKET JOINT. A joint in which spherical 
object is placed within a socket made to fit it. 

BALL BEARING. A bearing whose journal works upon a 
number of metal balls and thus reduces friction. 

BALLISTICS. The science dealing with the velocity, path 
and impact of projectiles. 





300 TEXT BOOK ON RADIO 


BALLISTIC GALVANOMETER. A galvanometer used for 
measuring short duration currents. Used for measuring a 
condenser discharge. 

BAR MAGNET. A straight bar of steel with both ends mag¬ 
netized. 

BAROMETER. A meter for measuring the pressure of the 
atmosphere. 

BARS, COMMUTATOR. The bars of copper or bronze, mak¬ 
ing up the segments of a commutator of a dynamo or motor. 

BARRETTER. A thermal detector. 

BASE PLATE. The plate used as a foundation. 

BATTERY. A combination of elements for the production of 
storage of electrical energy. 

BATTERY, DRY. An open circuit battery containing solified 
zinc oxychloride of gelatinous siliqa. 

BATTERY GAUGE. A small galvanometer for testing bat¬ 
teries and connections. 

BEARING. The support on which the moving part of a 
machine rests. 

BEARING SURFACE. The surface of bearing parts which 
are in mutual contact. 

BEAUMES HYDROMETER. A hydrometer named after its 
maker; used to measure liquids lighter than water. 

BED PIECE. The frame carrying a dynamo or motor. 

BERNE BUREAU. Bureau of the international Telegraph 
Union at Berne, Switzerland. 

BICHROMATE CELL. Two carbon plates immersed in a solu¬ 
tion of sulphuric acid, bichromate of potash and water. 

BIFURCATION. Spreading into two branches. 

BILLI CONDENSER. A variable tubular condenser. 

BINDING POSTS. Metal fixtures fitted to receive the ends 
of wires and thus make electrical contact. 

BISMUTH. One of the elements that is a conductor of elec¬ 
tricity. 

BOARD OF TRADE UNIT. An English standard, 1,000 
watt hours, equal to one and one-third horse power; written 
B. O. T. 

BLIND FLANGE. A plate used to cover an orifice. 

BLUE STONE. Crystallized copper sulphate. 

BOLOMETER. An apparatus similar to Wheatstone Bridge. 

BORE. The interior diameter of a cylinder. 

BOOSTER. A dynamo used to raise the pressure of another 
dynamo. 

BRADFIELD INSULATOR. A leading-in insulator; an 
ebonite tube fitted with ebonite spark discs made to prevent 
rain running down and making a ground connection. 





EADIO TEEMS 


301 


BEASS. An alloy of seven parts copper and three parts zinc. 

BRAZING. The process of joining metals together. 

BEAZING METAL. An alloy of tin and zinc. 

BEEAKEE. A switch or other device for opening a circuit. 

BEONZE. An alloy of copper, tin and lead. 

BROWN AND SHAEPE GAUGE. A wire gauge of American 
standard. 

BRUSH. A rod of carbon held in a holder and pressed against 
the commutator. 

BRUSH HOLDER. An adjustable clamp into which the 
brushes are fixed and then held against the commutator. 

BRUSH, WIRE. A brush made of rolled wire gauze. 

B. T. U. British Thermal Unit. 

BUFFING WHEEL. A wheel covered with leather and 
mounted so it can be rotated; used for polishing. 

BUS BAR. A heavy copper conductor used on distribution 
boards. 

B. W. G. Birmingham Wire Gauge. 

CABLE—A heavy electrical conductor highly insulated. 

CALL BELL. A bell used to attract the attention of the 
person called. 

CAM. A revolving disc rotated on a shaft or spindle and 
shaped to give a variable motion to the driven element. 

CAM FRICTION. The friction between the cam and the 
element it actuates. 

CANADA BALSAM, A gum used in cementing lenses. Ob¬ 
tained from balsam fir. 

CAPACITY. The extent of space; power of containing. 

CARRYING CAPACITY. The capacity of an electrical con¬ 
ductor to carry current without overheating. 

CARBON. One of the elements; exists in three forms—char¬ 
coal, graphite and diamond. It is used as an electrical con¬ 
ductor, for arc lamps and incandescent lamp filaments.^ The 
carbons used for arc lamps generally have a core of soft 

powder carbon. • 

CARBORUNDUM. An artificial silicate of carbon produced 
under very high temperature; often used as crystal de¬ 
tector. 

CARTRIDGE FUSE. A safety device; fuse wire enclosed ir 
a cardboard tube with metal ends. 

CASCADE. A number of Leyden jars connected m series. 

CATHODE. The terminal of an electrical circuit. 

CAT WHISKER. The fine wire used on a crystal detector. ^ 

CENTIGRADE. A thermometer scale; freezing point 0°; 
boiling point 100°. 

CENTIMETER. Unit of length, 0.3937 inch. 





302 TEXT BOOK ON RADIO 


CENTRAL STATION. A point from which current is sent 
out. 

CENTBIFUGAL FOBCE. The force which draws a body con¬ 
strained to move in a circular path, away from the centre 
of rotation. 

CHARACTERISTICS OF SOUND. A, pitch; b, loudness; c, 
quality. 

CHARGE. A quantity of electricity at rest, measured by units 
of quantity such as the coulomb. 

CHECK UNIT. Generally called lock nut, a nut placed over 
another nut on the same bolt to lock the main nut in 
place. 

CHLOBIDE. A non-inflammable gas, Atomic weight 4.90. 
Specific Gravity 1.4. 

CHOKE COILS. Coils of wire wound on an iron core some¬ 
times called induction coils. 

CHBONOSCOPE. An instrument for measuring very short 
intervals of time. 

CIRCUIT. The path through which the current flows. 

CIBCUIT-BREAKEB, AUTOMATIC. A device, a circuit. 

CIBCUIT, CLOSED. A circuit closed so as to give the current 
a continuous path. 

CIBCUIT, OPEN. A circuit with its continuity broken, as by 
the opening of a switch. 

CIRCUIT-BEEAKEB, AUTOMATIC. A device that auto¬ 
matically breaks the circuit in case of overload. 

CIRCUIT, GROUNDED. A circuit where t' e return wire 
is done away with so that the earth completes the circuit, 
as in wireless work. 

CIRCULAR MIL. Unit of area, the area of a circle "whose 
diameter is one mil. 

CLEAT. A wood, porcelain or composition support for wires. 

CLOCKWISE. A machine or other device that runs in a 
right hand direction; that travels as do the hands of a 
clock. 

CLOTH WHEEL. A polishing wheel. 

CLUTCH. A device for engaging or disengaging two pieces 
of shafting. 

CODE, CIPHER. A code of prearranged words, letters or 
signs. 

CODE, TELEGRAPHIC. An alphabet made up of dots and 
dashes. 

COIL. A series of rings or turns of wire. 

COIL, INDUCTION. Built the same as a transformer; has 
a laminated iron core and a primary and secondary coil. 





EADIO TEEMS 


303 


COIL, RESISTANCE. A coil of some poor conducting metal 
wire such as German silver. Used to offer resistance to 
the flow of current. A rheostat. 

COINCIDE. Two or more articles that occupy the same place 
in space. 

COLLET. A metal ring used to retain metallic packing in a 
stuffing box. 

COMMUTATOE. That part of a dynamo which changes the 
direction of the current. 

COMPASS, EADIO. An apparatus used to find the location 
of a radio transmitting or broadcasting station. 

COMPOUND. A mixture of two or more elements. 

COMPOUND WOUND GENEEATOE. A dynamo giving a 
constant electromotive force, on account of having its field 
magnet winding partly in shunt with current generated. 

CONDENSEE. An appliance for storing up electrical energy, 
made of a number of thin sheets of tin foil laid on top of 
each other and separated from each other by an insulator. 
Condensers in multiple will increase the total capacity. Con¬ 
densers in series will decrease total capacity. 

CONDENSEE, ADJUSTABLE. A condenser, part of which 
may be cut in or out of the circuit, thus varying its ca¬ 
pacity. 

CONDUCTANCE. The conducting property of any material. 

CONDUCTOE. Anything that will permit the passage of elec¬ 
tricity—a wire. 

CONDUCTIVIT The reciprocal of the ohm. Unit is the 
Mho, (Ohm written backwards). 

CONDUIT. A metal pipe through which electrical conductors 
are run. 

CONTACT, ELECTEIC. A contact between two conductors 
giving a continuous path for the current. 

CONTACT BEEAKEE. Any appliance for quickly opening or 
closing a circuit. 

CONSTANT LOAD. A load whose pressure is steady and in¬ 
variable. 

CONTINUOUS. Uninterrupted, without break or interruption. 

CONTINUOUS CURRENT. Direct current. A current that 
always runs in the same direction. The opposite to alter¬ 
nating current. 

CONTINUOUS WAVES. Waves whose amplitude are con¬ 
stant. Waves produced by frequency multiplying trans¬ 
formers. 

CONVERTER. An electric machine or apparatus for chang¬ 
ing the potential difference of an electrical current. 





304 


TEXT BOOK ON RADIO 


COPPER. A metal; one of the elements; a good conductor 
of electricity. 

CORE. The iron centre of a transformer, on which the pri¬ 
mary and secondary coils are wound. 

CORE DISCS. Thin metal discs used in building up armature 
cores, etc. 

COTTER PIN. A headless split pin. 

COUPLING WAVES. The two waves produced by coupling 
the oscillating circuits. 

CORROSION. Chemical action which causes destruction of 
metals, usually by oxidation or rusting. 

CORRUGATED. Formed with a surface consisting of alter¬ 
nate valleys and ridges. 

COULOMB. The practical unit of quantity of electricity. It 
is the quantity passed by a current of one ampere intensity 
in one second. 

COUNTER CLOCK WISE. A machine that runs from right 
to left, the opposite direction to the hands of a clock. 

COUPLING. The connection of two oscillating circuits. 

CRATER. The depression that forms in the positive carbon 
of a voltaic arc. 

C. P. Abbreviation for Candle Power. 

CRYSTAL DETECTOR. A detector using a crystal and thin 
metal wire to rectify a number of oscillations. 

CURRENT. A current of electricity is supposed to flow from 
the positive pole of a generator, through the various ap¬ 
pliances in the circuit and back to the generator through 
the negative pole. The unit of current strength is the 
ampere. 

CURRENT, ALTERNATING. A current that -is continually 
changing both its strength and direction. A current that 
changes its flow of direction so many times a second ac¬ 
cording to the construction of the alternator. These changes 
are called cycles. 

CURRENT, DIRECT. A current that always flows in the 
same direction. The opposite to Alternating Current. 

CURRENT FREQUENCY. The number of times alternating 
current changes its flow of direction in a second. These 
changes are called cycles. 

CURRENT, INDUCED. A current produced in a conductor 
by induction. 

CURRENT, NEGATIVE. The current which deflects the 
needle to the left in a single needle telegraph system. 

CURRENT, POSITIVE. The current which deflects the 
needle to the right in a single needle telegraph system. 










EADIO TEEMS 


305 


CUEEENT EEVEEjSEE. Some appliance, generally a switch 
for changing the direction of a current in a conductor. 

CUEEENT, SECONDAEY. The current induced in the sec¬ 
ondary coil of a transformer or induction coil. 

CUT-OUT. Either a fuse or a magnetic control arranged to 
open a circuit should the circuit be overloaded. 

CYCLE. A term given to the alternation of an alternating 
current circuit. 

DASH COIL. An induction coil for jump spark ignition. 

DAMPING. The weakening of amplitude in a train of electro 
magnetic waves owing to resistance and radiation from an 
oscillating circuit. 

D. C. Direct Current. (See “Current, Direct”) 

DEAD BEAT. Where the moving indicator of measuring in¬ 
struments comes to a. reading quickly, without the indicator 
oscillating. 

DELTA GEOUPING. A way of connecting up three phase 
windings in the form of a triangle. 

DETECTOE. An apparatus that changes the oscillations re¬ 
ceived by the aerial into audible sounds. 

DETEBIOEATION. The state of growing worse. 

DEVIATION. Divergence from a course. 

DIAPHEAGM. A thin iron disc in the telephone receivers 
which is thrown into motion by electric impulses and 
changes the vibrations to audible sounds. 

DIELECTBIC. A non-conductor of electricity. 

DIFFBACTION. The bending of electro magnetic w r aves 
around the earth’s curvature. 

DIMMEE. An adjustable choking coil used to regulate the 
intensity of electric incandescent lamps. 

DIEECT CUEEENT. A current of uniform strength that al¬ 
ways flows in the same direction. 

DIEECT COUPLING. A coupling where the inductance coils 
of both currents are directly connected. 

DIBECTION. The direction of an electric current is sup¬ 
posed to be from the positive pole to the negative pole of 
the circuit. 

DIBECTION FINDEE. See Eadio Compass. 

DIBECTIVE AEEIAL. See Bellini Aerial. 

DIEECT LOOSE COUPLING. A coupling where two induct¬ 
ance coils, though directly connected, are at a distance from 
each other, or a coupling where only a few turns are com¬ 
mon to both circuits. 

DIEECT TIGHT COUPLING. A coupling where one circuit 
has its inductance formed by tapping off a number of 
turns from the coil actually employed as inductance in the 
other circuit. Also called Direct Close Coupling. 


20 








306 TEXT BOOK ON BADIO 


DISC CONDENSER. A variable condenser with its two sets 
of plates composed of semi-circular inter-leafing metal 
vanes, separated by insulating discs or air; the whole being 
mounted in a circular case, one set of vanes is fixed, the 
other mounted on an insulated spindle is capable of being 
turned through an angle of 180 degrees, thereby permitting 
of any desired amount of interleafing of vanes; thus regu¬ 
lating the amount of capacity. 

DISCHARGE. To dissipate electric energy from a condenser 
or battery. 

DISTANCE SPARKING. The distance between electrodes 
which a spark from some source will jump. 

DISTRIBUTION BOX. A metal box or cabinet containing 
a distribution panel together with fuses, switches, etc. 

DOUBLE POLE SWITCH. A switch with two knife like 
blades, able to break both the positive and negative wires 
of a circuit. 

DOWNDEAD. The wire connecting the aerial to the instru¬ 
ments. 

DRY CELL. An enclosed battery used for open circuit work. 

DUPLEX. Twofold, working two ways. 

DYNAMICS. The mechanics of moving forces or motion, the 
reverse of static. 

DYNAMO. A machine used to convert mechanical energy into 
electrical energy. 

DYNE. Unit of force. 

DYNOMETER. A meter for measuring mechanical force. 

EARTH. Generally refers to a connection to the earth. An 
accidental grounding of a conductor. 

EBONITE. Vulcanized India rubber; a non-conductor of heat 
and electricity. 

ECONOMIZER. A step-down transformer. 

EFFICIENCY, MECHANICAL. The rate between the work 
performed and the energy expended by the machine in 
performing it. 

ELECTRICITY. An unknown power; a powerful physical 
agent which manifests itself mainly by attraction and re¬ 
pulsion; also by luminous and heating effects, by violent 
commotions, by chemical decompositions and many other 
phenomena. The word was first used by Dr. Gilbert in 
England during the Sixteenth Century. 

ELECTRICS. Certain substances can be electrified by fric¬ 
tion. 

ELECTRODE. The terminal of an open electric circuit. 

ELECTRODYNAMICS. Electricity in motion. 





RADIO TERMS 


307 


ELECTROLYSIS. The breaking up of a compound into its 
elements by the use of an electric current. 

ELECTRIC HORSE POWER. 746 watts are equal to one 
unit of Electric Horse Power. 

ELECTROLYTIC DETECTOR. A fine wire making contact 
with an electric light. 

ELECTRO MAGNET. A mass of iron magnetized by winding 
around it several coils of copper wire. The softer the 
iron the more easy it is to magnetize. Hard metals retain 
their magnetism longer. 

ELECTRO MOTIVE FORCE. Another term for electric pres¬ 
sure or voltage. 

ELECTROSCOPE. Apparatus for detecting static charges of 
current. 

ELEMENT. There are about seventy-five known elements. 
Is an original form of matter that cannot be divided into 
constituents by any process. 

EMBOSSER, TELEGRAPH. A receiver which embosses tele¬ 
graphic paper tape. 

EMERGENCY APPARATUS. A second generator set that 
can be used in case of trouble. 

EMERY WHEEL. A machine used for grinding. 

E. M. F. Electro Motive Force. Voltage. Pressure. 

ENERGY. Capacity of acting; energy may be mechanical, 
electrical, chemical, physical, etc. Unit of energy is the 
ERG. 

ENERGY, ELECTRIC. Unit is the volt coulomb or volt am¬ 
pere. 

EQUIDISTANT. Placed at equal distance from the same 
point. 

EQUIVALENT, ELECTRO-CHEMICAL. The weight of a 
substance set free by one coulomb of electricity. 

ERG. The unit of work. The amount of energy expended in 
moving a body through one centimeter against a resistance 
of one dyne. 

ETHER. A name given by Huygens to the medium that fills 
all space and matter. 

EXCITER. A dynamo used to excite the fields of a gener¬ 
ator. . . 0 

FAHRENHEIT. A thermometer scale. Freezing point is 3z . 

Boiling point, 212°. 

FATHOM. A measure of length; six feet. 

FARAD. Practical unit of capacity. 

FEEBLY DAMPTED. A train of oscillations with many 
complete oscillatory motions. 

FEEDER. A main wire or set of wires. 





308 


TEXT BOOK ON RADIO 


FEEDER, NEGATIVE. The wire connected to the negative 
pole of a generator. 

FEEDER, NEUTRAL. The wire connected to the middle or 
neutral point in a three-wire system. The w r ire common 
to both generators. 

FEEDER, POSITIVE. The wire connected to the positive 
pole of a generator. 

FIELD MAGNETS. Electric magnets that produce the mag¬ 
netic field in which the armature of a generator rotates. 

FIELD REGULATOR. A variable resistance. 

FLATS. Comihutator segments worn to a lower level than 
other segments. 

FLAT TUNING. The considerable adjusting of tuning with¬ 
out altering the strength of the signals. 

FLUX. A compound used in soldering. 

FOOT POUND. The resistance equal to one pound moved 
upwards one foot. 

FORCE. May be defined as the rate of change of momentum. 

FREAK. The increasing or decreasing of range of signals 
that periodically happens to a receiving set. 

FREQUENCIES, RADIO. Radio frequencies are very high, 
sometimes as high as 1,500,000 cycles per second. 

FUNDAMENTAL WAVELENGTH. Ordinary wavelength of 
a circuit. 

FUSE. A short length of fusable wire introduced into a 
circuit as a safety device. 

FUSING POINT. The temperature at which metals melt and 
become liquid. 

GALENA. A crystal sulphide of lead. When heated becomes 
lead sulphate. Used as a thermo-electric detector. 

GALVANIZED IRON. Iron with a coating of zinc to prevent 
rusting. 

GALVANOMETER. An instrument for measuring current 
strength and direction of current in a circuit. 

GAP. An opening by breaking or parting. 

GAP MICROMETER. A gap to protect apparatus from over¬ 
loads. 

GASKET. A ring or washer used for packing or insulating. 

GAUGE. An instrument to measure size or capacity. 

GAUZE WIRE. A pliable wire cloth made of very fine strands 
of wire. 

GEISSLER TUBE. A vacuum tube having its electrodes in 
bulbs. 

GENERATOR. An apparatus for maintaining an electric cir¬ 
cuit. 








EADIO TEEMS 


309 


GEEMAN SILVEE. Alloy of nickel and copper with a per¬ 
centage of zinc. Used in resistance frames, rheostats, etc. 

GOLD. One of the elements; a conductor of electricity. 

GONIOMETEE. An instrument for measuring angles. 

GEAM. The unit of weight. Equal to 15.43 grains. 

GEAPHIC TELLUEIUM. A crystal rectifier. 

GEAPHITE. A soft form of carbon, used as a lubricant. 

GEAYITY. The attractive force of the earth. 

GEID. A frame of wire gauze found between the plate and 
filament of a vacuum tube. Perforated lead plate used in 
storage batteries. 

GEID LEAK. A form of rheostat to permit excess grid 
charges to escape to an external source. 

GEOUND. The contact of an electrical conductor with the 
ground or with some other conductor not in the circuit. 

GEOUND CLAMP. A strip of copper for making an easy 
and secure connection with a water pipe, etc. 

GEOUND WIEE. The wire leading from the aerial to the 
ground. The wire used as a return wire of the circuit in 
wireless work. 

GUN METAL. A compound of nine parts copper and one 
part tin. 

GUTTA PEECHA. The hardened juice of the Isonandra 
Gutta, used as an insulator. 

GUY EOPES. Eopes or wires used to steady the aerial 
supports. 

HAND ®E WING NUT. A nut with flanges allowing it to 
be tightened by hand. 

HEAT. A physical kinetic form of energy. 

HELIOGEAPH. A mirror for reflecting flashes of light, gen¬ 
erally the Sun’s rays; used in signal work. 

HELIX. A coil of wire. 

HENEY. Unit of inductance. 

HEETZIAN WAVES. Ether waves. 

HIGH FEEQUENCY. A current with a very great number 
of alternations per second. 

HIGH FEEQUENCY SLIDING INDUCTANCE. Two metal 
bars connected by a sliding brass clamp used for making 
final adjustment in closed oscillatory circuits. 

HIGHLY DAMPED TEAIN. A train with few oscillations. 

HONEY-COMB COIL. A tuning coil. A set of three coils— 
primary, secondary and tickler; the primary coil being 
placed between the other two. 

HOESE POWEE. A unit of rate of work. Equal to the rais¬ 
ing of 33,000 pounds one foot in one minute. Equal to 
746 watts. 





310 


TEXT BOOK ON RADIO 


HORSE POWER HOUR. One horse power exerted for one 
hour. 

HORSE SHOE MAGNET. A steel bar shaped like a horse 
shoe with its ends magnetized. 

HUMIDITY. The dampness in the atmosphere which varies 
with the temperature. 

HYDROELECTRIC GENERATOR. A generator driven by a 
turbine. 

HYDROMETER. An instrument used to test the specific 
gravity of a fluid. Used for testing the discharge of 
storage batteries. 

HYPOTHESIS. Taken for granted. Assumed for the pur¬ 
pose of argument. 

HYSTERESIS. A reluctance when a change of condition is 
taking place in a circuit. 

IMPEDANCE. The total opposition of a circuit, due to re¬ 
actance and resistance to a varying circuit. 

IMPEDANCE COIL. Another name for induction coil, an 
iron core around which is wound a coil of wire. 

INCANDESCENCE, ELECTRIC. The heating of a conductor 
to a white heat. 

INCH. The twelfth part of a foot. A measure of length. 

INCLINATION. A tendency from the true horizontal or ver¬ 
tical direction, as in the case of the compass needle. 

INDUCTANCE. The induction of a current in a non-electrical 
body from an electrified or magnetized body, without me¬ 
tallic or electrical connection. 

INDUCTION COIL. A transformer; an apparatus for chang¬ 
ing low voltage to high voltage. 

INDUCTIVE COUPLING. The coupling of two oscillatory 
circuits by arranging the inductance coil of one circuit into 
the lines of force of the other circuit. 

INDUCTIVE LOOSE COUPLING. A coupling without me¬ 
tallic contact and where the inductances are well apart. 

INDUCTOR. A step-down transformer. 

INERTIA. Property of matter at rest. 

INSULATING TAPE. A prepared tape to cover and insulate 
ends of wires when making joints, etc. 

INSULATOR. Any material that will not allow the passage 
of electricity through it, except under very great pressure. 

INTENSITY. The strength of a current, expressed in am¬ 
peres. 

INTERFERENCE. Where more than one set of electro mag¬ 
netic waves arrive in such a manner as to nullify each other. 

INTERMITTENT. Acting at intervals. 






RADIO TERMS 


311 


INTERSECTION". The place where two wires cross each other. 

INVERTED “L” AERIAL. An aerial that is tapped at one 
end by the lead in wire. 

IRON. A metal; one of the elements. 

JAMMING. QRM. Interference from other stations. 

JIGGER. An oscillation transformer. 

JOULES. Unit of electrical w T erk. Volt coulomb. 

JOURNAL. That part of a shaft or spindle which rotates 
in the bearings. 

KEY TRANSMITTER. An easily controlled switch which al¬ 
lows the operator to rapidly make and break the primary 
circuit. 

KILOWATT. One thousand watts. Written K. W. 

KNIFE SWITCH. A switch with knife like blades, used on 
circuits carrying high amperage. 

LAG SCREW. A wood screw with a square head. 

LAMINATED. Made up of a number of fine sheets. 

LATERAL FORCE. Force proceeding from the side. 

LAW OF MAGNETISM. Like poles repel one another. Un¬ 
like poles attract each other; positive pole attracts nega¬ 
tive, etc. 

LEADING-IN INSULATOR. An insulation tube used in the 
walls or roof through which the lead-in wi' e from aerial 
runs. 

LEAKAGE. A loss of current due to _ oor insulation or other 
causes. 

LENZ LAW. An induced current always tends to stop the 
current which produces it. 

LEYDEN JAR. A static condenser. 

LIGHT. Light waves travel at the same rate of speed as elec¬ 
tro magnetic waves; 186,000 miles per second. Light is 
merely ether vibrations. 

LIGHTNING ROD. A metal rod connected with the earth, 
used on buildings as a safety device. 

LINES OF FORCE. Imaginary lines showing the direction 
of attraction and repulsion in a field of force. 

LINK FUSES. A link of fusable metal, introduced into the 
circuit as a protective device. 

LOADING COIL. A single slide, tuning coil. 

LOCAL CURRENTS. Currents within the metal parts of a 
generator. 

LOCK NUT. A nut placed over another nut on the same 
bolt to hold the original nut in place. A check nut. 

LODESTONE. An iron ore which possess the properties of 
a magnet. Also known as Magnetite. 










312 


TEXT BOOK ON BADIO 


LOG DECREMENT. The hyperbolic log of reciprocal of the 
ratio of the first amplitude to second amplitude in a train 
of waves. 

LOOP AERIAL. A frame around which several turns of wire 
are wound. 

LOOSE COUPLING. A coupling without metallic contact 
or where the inductances are well apart. 

LOST MOTION. The motion in a machine that produces no 
useful results. 

LOW FREQUENCY. A current whose alternations are low 
per second. 

LUBRICANT. Anything used to help diminish friction be¬ 
tween two or more working parts; like oil, graphite, etc. 

LUGS. Metal wire terminals. 

MAGNET. A piece of iron or steel that has the property 
to attract or repel other pieces of metal. 

MAGNET COIL. The coil over an iron core in an electric 
magnet. 

MAGNETIC FIELD. The field or space over which the 
magnet exerts its influence. 

MAGNETIC FLUX. The lines of force which flow from a 
magnet; magnetic induction. 

MAGNETIC FORCE. Force at any point in a magnetic 
field. 

MAGNET HORSE SHOE. A bar of steel shaped like a horse 
shoe with both ends magnetized. 

MAGNETIC LIMIT. The temperature beyond which a metal 
cannot be magnetized. 

MAGNETIC SELF INDUCTION. A magnet tends to repel 
its own magnetism and weaken itself by self-induction. 

MAGNETITE. A natural magnetic iron ore. Lodestone. 

MAGNETO. A small generator. 

MAKE AND BREAK CURRENT. A current continually 
broken and started again as is the action in an induction 
coil. 

MALLEABLE. Capable of being worked into shape. 

MANGANESE BRONZE. An alloy of copper, tin and fer¬ 
romanganese ore. 

MANGANESE STEEL. An alloy of steel and metal manga- 
neS e. 

MARCONI FILINGS COHERER, A glass tube containing 
fine metallic filings used as a detector. 

MEGAPHONE. An instrument used to help make the voice 
audible at a distance. 

MEGOHM. One million ohms. 






RADIO TERMS 


313 


MERCURY. A metallic element liquid at ordinary tempera¬ 
ture; also known as quicksilver. 

METER VOLT. An instrument for measuring the pressure 
or voltage of a circuit. Connected in multiple on your 
line. 

METER AMPERE. An instrument for measuring the flow 
of current. 

METER WATT. An instrument for measuring the wattage. 
Volts times amperes. 

MHO. Unit of Conductivity. The word ohm spelled back¬ 
wards. 

MICA. A mineral more or less transparent and used as an 
insulator. 

MICANITE. A manufactured insulator made of mica. 

MICRO. One millionth. 

MICROFARAD. Unit of capacity. 

MICROHM. One millionth of an ohm. 

MICROMETER. An instrument for measuring small distances 
like the thousandth or ten thousandth part of an inch. 

MICROMETER SPARK GAP. An adjustable spark gap used 
in the aerial circuit. 

MICROPHONE. An apparatus to magnify sound. 

MIL CIRCULAR. A unit • of area. The area of a circle 
whose diameter is one mil. 

MIL FOOT. A unit, of resistance. A wire one foot long 
with a diameter of one mil. 

MILLIMETER. A unit of length. One thousandth part of 
a meter. 

MINIMUM. The least quantity. 

MOLECULE. The smallest part of an element that can exist 
alone. 

MOLYBDENITE. A sulphide of Molybdenum. Used as a de¬ 
tector. 

MORSE RECEIVER. A receiver named after S. F. B. Morse. 

MORSE INKER. An instrument that records the received 
message on a traveling paper tape. 

MOSCISKI CONDENSER. A condenser in the form of a 
glass tul^e with a metal foil coating. 

MOTOR. A machine to convert electrical energy into me¬ 
chanical energy. 

MOTOR GBNERATOR. A combined motor and generator; 

a generator driven by a motor. . ' 

MOTOR SERIES. A motor whose armature windings and 

field windings are in series. > 

MULTIPLE. Multiple connection is that m which each lamp 
draws its supply direct from the mains and is not de- 





314 


TEXT BOOK ON RADIO 


pending on any other lamp or set of lamps for its supply. 
Lamps in parallel with each other. The opposite to 
series* 

MUTUAL INDUCTION. The introduction of an electrical 
pressure in a circuit, by another circuit not directly con¬ 
nected to it. 

NATURAL CURRENTS. Earth currents. 

NATURAL WAVELENGTH. The natural length of wave 
produced by the aerial’s own capacity and inductance. 

NEGATIVE. The opposite to positive. The pole to which 
the current seems to flow. 

NEGATIVE CHARGE. One of the two electric charges, the 
opposite to positive. 

NEUTRAL WIRE. The middle wire of a three wire system. 
The wire that is common to both dynamos. 

NICKEL SILVER. An alloy of nickel, copper and zinc. Ger¬ 
man silver used in making resistance coils. 

NICKEL STEEL. Steel with the addition of a small per¬ 
centage of nickel. 

NON-CONDUCTOR. Any material that will not conduct elec¬ 
tricity. 

NON-INDUCTIVE CIRCUIT. A circuit possessing a very 
small inductance. 

NOTCH WIRE GAUGE. A gauge with notches for measur¬ 
ing wire. 

OHM. Unit of electrical resistance. The resistance offered 
by a column of pure mercury, 106.3 centimeters in length 
by one square millimeter in cross section at a temperature 
of zero centigrade. 

OHM’S LAW. The fundamental principle on which all elec¬ 
trical mathematics are worked. The current in amperes 
is equal to the voltage divided by the resistance in ohms. 
The resistance is equal to the voltage divided by the cur¬ 
rent in amperes. The voltage is equal to the resistance in 
ohms times current in amperes. Thus with two known 
quantities you can always find the third unknown. 

OHMIC RESISTANCE. True resistance. 

OSCILLATING CURRENT. An alternating current of high 
frequency. 

OSCILLATOR HERTZIAN. A device for producing oscilla¬ 
tions. 

OSCILLATORY INDUCTION. Induction produced by action 
of an oscillatory discharge. 

PAPER CONDENSER. A condenser made with tin foil and 
paraffin paper. 

PARTITION INSULATOR. A leading-in insulator. 








RADIO TERMS 


315 


PERIOD. Time required to produce aud complete one wave; 
time required to complete one cycle of an alternating current 
circuit. 

PERIPHERY. The circumference of a circle. 

PERMANENT MAGNET. A magnet that will retain its mag¬ 
netism away from the source of magnetism. 

PHENOMENON. An unusual occurrence. 

PHONETRON. A trade name for a type of amplifying tele¬ 
phone receiver. Consists of an enclosed electro-magnetic 
solenoid producing an annular field in which an armature 
coil is suspended from the apex of a conical diaphragm. 
The magnet requires a current of 2 y 2 amperes at a pressure 
of 6 volts. 

PHOSPHOR BRONZE. A very hard alloy of copper, tin and 
phosphorus. 

PLUNGER. A movable core used with a solenoid to be drawn 
in an oil bath when the coil is excited. 

POLARITY. Pertaining to the poles of a circuit; the positive 
and negative. 

POLARIZATION. The changing of a voltaic cell by depriv¬ 
ing it of its proper pressure. 

POLYPHASE. More than one phase. Multiphase. 

POSITIVE POLE. The pole from which the current is sup¬ 
posed to start on its journey around the circuit. 

POTENTIAL. The pressure of an electric charge. 

POTENTIOMETER. An arrangement for determining po¬ 
tential difference. 

POUNDAL. British unit of force. 

POWER. Activity; rate of doing work. 

PRIMARY COIL. The coil of a transformer that is connected 
to the source of supply. 

PRIMARY COLORS. Red, yellow, blue. 

PRIMARY POWERS. Water power; wind power; tide power; 
power of combustion; power of vital action. 

PRIMARY TUNING INDUCTANCE. A variable inductance 
in the primary closed oscillatory circuit. 

PROPAGATION. The traveling of electro-magnetic waves 
over the earth’s surface. 

PROTECTIVE ROD. A carbon rod of high resistance con¬ 
nected into the circuit as a safety measure. 

PYROMETER. A meter for measuring excessive heat. 

QUADRANT. A quarter of a circle; an angle of 90 degrees. 

QUARTZ. A hard rock of native silica. 

QUENCHED SPARK. A spark gap made of a series of 
metal plates insulated from each other. 

QUICKSILVER. Mercury; a liquid metal. 





316 


TEXT BOOK ON RADIO 


RADIAL. Spreading from a centre. 

RADIATION. The transmission of ether waves through 
space. 

RADIATING CIRCUIT. The aerial circuit. 

RADIO TELEPHONY. Transmission of speech by electro 
magnetic waves. 

REACTANCE. The opposition offered to the flow of current 
by back electro motive force, etc. 

REACTANCE COIL. An adjustable iron core around which 
is wound a coil of wire. 

REACTION. Inverse action. 

RECTIFIER. An apparatus for changing alternating current 
to direct current. 

REFRACTION. The change in direction or bending of the 
electro magnetic waves. 

REGENERATIVE CIRCUIT. A reactionary circuit. 

RECEIVING DETECTOR. A device to change the charac¬ 
teristics of incoming oscillations so as to make them 
audible. 

RECEIVING TUNER. An oscillation transformer which al¬ 
lows the operator to receive electro magnetic w r aves of dif¬ 
ferent lengths. 

RELAY. An instrument consisting of an electro-magnet 
which actuates upon receiving a current and in actuating 
opens and closes a circuit. 

RELUCTANCE. The resistance offered to the flow of lines 
of magnetic force. 

RESISTANCE. That property of an electrical conductor 
which tends to oppose the flow of current over it. Every¬ 
thing in a circuit offers resistance to the flow of current. 

RESISTANCE BOX. A box filled with resistance coils con¬ 
nected in series with each other; a resistance frame. 

RESISTANCE, OHMIC. True resistance. 

RESISTANCE, SPURIOUS. Counter electric motive force. 

RETARDATION. A retarding of the rate of transmission of 
signals. 

RESONATOR. A sound box. 

RETENTIVITY. Coercive force. 

RHEOSTAT. An instrument used to offer resistance to the 
flow of current. Made of a number of metal coils (German 
silver or iron) connected together in series and mounted 
on a frame from which the coils are insulated. 

RHUMKORFF COIL. An induction coil. 

ROTARY. Turning on an axis—rotating. 

RUBBER COVERED WIRE. A cable either solid or stranded 





RADIO TERMS 


317 


with a rubber covering and an outer protective covering of 
cotton braid. 

SAL AMMONIAC. Ammonium chloride. 

SECONDARY COIL. The coil of a transformer into which 
the current is induced. 

SERIES. An electrical connection where lamps are connected 
so that they depend one on the other for supply, the cur¬ 
rent passing through each lamp successively. The opposite 
to multiple. 

SET COLLAR. A ring used on a shaft or spindle to prevent 
end play. 

SEXTANT. An instrument used on board ship to measure 
angles. 

SHEET METAL GAUGE. A gauge to measure the thickness 
of metals. 

SHELLAC. A gum gathered from trees in India used in radio 
and electrical work in the form of a varnish. An excellent 
insulator. 

SHORT CIRCUIT. Two wires of opposite polarity coming in 
contact with one another without any controlling device. 

SHUNT. A shunt for the receiving relay consisting of the 
coils of an electro magnet. 

SHUNT WINDING. A system of winding where the arma¬ 
ture winding is in parallel with the field winding. 

SILICON. A mineral. Used as a detector. 

SINGLE PHASE. Using only two wires and one electromotive 
force; sometimes called monophase. 

SIXTY CYCLE A. C. This is when the current changes its 
flow of direction sixty times a second. This frequency is 
used a great deal for lighting and power purposes. 

SLIDING FRICTION. The friction that exists between mov¬ 
ing parts in sliding contact with each other. 

SLIP RINGS. Two rings on an alternator that take the 
place of a commutator on a direct current dynamo. 

SOLENOID. An electro magnet without the iron core. 

SPARK COIL. An insulated wire wound around an iron 
core, used for producing a spark from a source of low 
pressure. * 

SPARK GAP. The space between the ends of an electric 
resonator across which the spark jumps. 

SPECIFIC GRAVITY. The density of a solution against that 
of another, using water as a standard. 

SPECIFIC RESISTANCE. Resistance of any material having 
a cube of one centimeter. 

SPIRAL WINDING. The system of winding used on a ring 
armature. 





318 


TEXT BOOK ON RADIO 


STAGE CABLE. A cable containing twin conductors each in¬ 
sulated from the other and the whole covered with a com¬ 
position covering. 

STAND-BY. A position of tuning, allowing the reception of 
waves of various lengths. QRX. 

STANDARD CELL. The Weston Cell is now used as the 
standard. 

STARTING BOX. An adjustable resistance to regulate the 
flow of current when starting up the motor. 

STATIC. Atmospheric disturbance. 

STATIC CHARGE. An electric charge at rest. 

STATIC LEAK. A co'1 of wire used in the aerial circuit of 
tuner to allow atmospherics to leak to earth. 

STATIC TRANSFORMER. A transformer without moving 
parts. 

STATOR. The stationary part of an induction motor or gen¬ 
erator. 

STEEL. Iron hardened by the addition of carbon and manga¬ 
nese. 

STEP DOWN TRANSFORMER. A transformer that steps 
down the voltage and raises the amperage; has a greater 
number of turns of wire in primary than in secondary. 

STEP UP TRANSFORMER. A transformer that steps up 
the voltage and lowers the amperage; has a greater number 
of turns of wire in the secondary than in the primary. 

STORAGE BATTERY. An accumulator. A number of cells 
for the storage of electricity. 

STORAGE CAPACITY. The number of ampere hours that 
can be got from a storage battery. 

SULPHATING. The formation of a lead sulphate in storage 
batteries. May be overcome by prolonged charging. 

SULPHURIC ACID. A compound of sulphur, hydrogen and 
oxygen. 

SWITCH. A device for opening or closing a circuit. 

SWITCH BOARD. A board to which the mains are led con¬ 
necting with bus bars, fuses and switches. 

SWITCH, DOUBLE POLE. A heavy switch that disconnects 
or connects two leads simultaneously. 

SWITCH, KNIFE. A switch with knife like blades used on 
circuits carrying high amperage. 

SWITCH, SNAP. A small switch made to give a sharp break 
used on house lighting circuits, etc. 

SWITCH, THREE WAY. A switch so constructed that by 
turning its handle connection can be made from one lead 
to either of two other leads and also so that connection 
can be completely cut off. 







KAMO TERMS 


319 


SYNCHRONOUS. Simultaneous; to correspond in time. 

SYNCHRONOUS MOTOR. A motor which runs in synchron¬ 
ism with the alternating current supply. 

“T” AERIAL. An aerial where the horizontal span is tapped 
in the middle by the lead-in wire; thus forming a letter T. 

TELEFUNKEN. German name for radio telegraphy. 

TERMINAL LUGS. Metal terminals for ends of wire used 
so that good and quick connection can be made. 

TESLA COIL. An oscillating transformer. 

THERM. A unit of heat. 

THERMAL DETECTOR. A detector which acts by heat 
energy. 

TOGGLE JOINT. An elbow joint. 

THREE WIRE SYSTEM. A system of distribution of electri¬ 
cal current where three wires instead of two sets of two 
wires are used. The middle or neutral wire acts as a 
positive for the one side and of the system and as the 
negative for the other side. The advantage of the system 
is the saving of copper. 

TICKLER COIL. A coil in the circuit of a vacuum tube re¬ 
ceiver to transfer a part of the oscillating plate current 
energy into the grid circuit to enable the vacuum tube to 
generate oscillations of high frequency. It is coupled to 
the secondary of the oscillation circuit. An inductance coil. 

TONE FREQUENCY. Spark frequency. 

TRANSFORMER. An apparatus used on an alternating cur¬ 
rent circuit to either raise or lower the voltage. Made of 
two coils of wire named the primary and the secondary 
coils and a laminated iron core. The coils are insulated 
from the core and from each other. The current enters the 
transformer through the primary coil and sets up a magnetic 
flux around the core; the secondary coil cuts the lines of 
magnetic force and thus a new current is induced in the 
secondary. 

TRANSFORMER COILS. The two coils in a transformer; 
primary and secondary. 

TRANSFORMER CORE. A core made up of thin iron plates 
laid one on top of the other. 

TRANSMITTER. An instrument used to produce sounds to 
be transmitted. 

TRANSYERTER. A trade name for a.motor generator. 

TUNING. The process of securing the maximum indication 
by adjusting the time period. 

TWO PHASE. An alternating current system of electrical 
distribution making use of two currents of different phase. 
Can be arranged with either three or four wires. 





320 


TEXT BOOK ON RADIO 


UNIPOLAR DYNAMO. A dynamo where one part of the 
conductor slides around the magnet. 

ULTRAUDION. An audion used in a circuit having a type 
of energy coupling so that a powerful relay action may 
be obtained. Its elements are connected in two circuits so 
arranged that the energy coupling may be obtained through 
a bridging condenser in its plate filament circuit. 

VACUUM. A space destitute of all substance. 

VACUUM TUBE. The name given to the highly exhausted 
glass tube containing three elements. Used for detector in 
radio work. 

VALVE AMPLIFIER. Audion type vacuum tube containing 
three electrodes. 

VALVE TUNER. A tuner used wuth a valve detector. 

VARIABLE CONDENSER. A condenser which allows of 
easy and quick adjustment. 

VARIO COUPLER. A device for varying the inductance in a 
circuit. The primary and secondary coils are connected 
magnetically but not electrically. 

VARIOMETER. A device for varying the inductance in a 
circuit. Made by connecting two inductances in series. 

VARLEYS CONDENSER. A static condenser. 

VELOCITY. The rate of motion of a body. 

VIBRATION PERIOD. In electrical resonance the period 
of a vibration in an electrical circuit. 

VOLTAGE. Electric motive force or pressure. 

VOLTMETER. An instrument used to measure the pressure 
of a circuit. 

VULCANITE. Vulcanized India rubber. 

WATT. The practical unit of electrical power. Amperes 
times voltage. 

WATT HOUR. Watts times length in hours. One watt ex¬ 
pended for one hour. 

WATT MINUTE. One watt expended for one minute. 

WATT SECOND. One watt expended for one second. 

WAVE CHANGER. A transmitting switch to change from 
one wave length to another. 

WAVES, ELECTRO-MAGNETIC. Ether waves due to electro¬ 
magnetic disturbances. 

WAVE LENGTH. The distance covered by a wave from the 
transmitting station before the next successive wave starts. 

WAVE TRAIN FREQUENCY. The total number of waves 
being produced or received per second. 

WAVE METER. An instrument to measure wave lengths. . 

WIRE GAUGE. A gauge for measuring the diameter of 
wires. 






INDEX 


A 

“A” Battery. 264 

A C Radiophone Circuit. 125 

Adjustable Filament Rheostat. 47 

Adjusting Receiving Sets. 177 

Adjusting Transmitting Sets. 103 

Aerial Construction . 71 

Aerial Outfit . 88 

Aerial Protective Device . 89 

Aerial Switch. 75 

Aerial Wire . 73 

Aerials . 59 

Aerials for Various Wavelengths. 59 

Aeriola Jr. 185 

Aeriola Sr. Receiving Set. 185 

Alternating Current. 38 

Alternator, The . 44 

American Radio Transmission Set. 108 

Ammeter Connections . 56 

Ampere . 23 

Ampere Hour . 23 

Apparatus for Reception of Electro-Magnetic Waves. . . . 169 

Apparatus for Undamped Wave Transmission. 107 

Armstrong Super Regenerative Circuit. 231 

Audio Frequencies . 43 

Audio Frequency Amplification . 153 

B 

“B” Battery. 271 

Balancing Sets . 28 

Basketball Varicoupler . 219 

Basketball Variometer . 217 

Batteries . 264 

Battery Polarity . 271 

Binding Posts . 92 

Break in Armature. 273 


21 


321 



































322 


TEXT BOOK ON RADIO 


Motion Picture Projection 

By JAMES E. CAMERON 

The Standard Authority on Motion Picture Projection 
Over 1000 Pages Over 400 Illustrations 

Bound in Flexible Leather 

This is a text-book written in simple style dealing with projection from 
A to Z and illustrated in a manner which simplifies the subject. 
No Technicalities, Yet Complete and Comprehensive 

READ WHAT THE CRITICS SAY: 


Exhibitors Trade Review: “The 
best book ever written on the 
subject of Projection.’’ 

Motion Picture News: “In com¬ 
parison with all other works on 
the market this book stands in 
a class by itself. Should be 
in the library of every projec¬ 
tionist. The price is not a 
criterion of its worth.” 

Samuel Kaplan, President Local 

306: “The best book on pro¬ 

jection on the market—no ex¬ 
ceptions.” 

Bureau of Economics, Dept, of 
Public Instruction, Washing¬ 
ton, D. C.: “By far the most 
complete manual we know of. 
The most complete work of its 
kind.” 

Harry Rubin, Chief Projectionist, 
Rialto, Rivoli and Criterion 
Theatres, N. Y. C.: “The 

most complete and comprehen¬ 
sive book on projection pub¬ 
lished. Should be in every 
projection room in the coun¬ 
try.” 

J. E. Robin, Renowned Projection 
Engineer: “A book that ranks 
second to none.” 

Wm. C. Franke, Asst. Gen’l. Mgr., 
Simplex Machine Co.: “Will 

be welcomed by all manufac¬ 
turers, dealers and projection¬ 
ists.’ ’ 

J. Crozen, General Electric Co.: 

“A text book indispensable to 
the projectionist.” 


George F. Perkins, Leading Ca¬ 
nadian Authority: “A book 
equally valuab.e to the be¬ 
ginner and expert.” 

Screen Magazine: “The differ¬ 
ence between an amateur and 
expert projectionist rests in a 
study of this valuable man¬ 
ual.” 

Richard Cassard, General Man¬ 
ager, Nicholas Power Co.: “A 
w'orthy successor to Mr. Cam¬ 
eron’s other works on projec¬ 
tion.” 

Art Smith, Chief Projectionist, 
Capitol Theatre, N. Y. C.: 

“Will increase the earning ca¬ 
pacity of every projectionist 
who reads it.” 

C. W. Johnson, Chief Projection¬ 
ist, Wm. Fox Theatres: 

“Everyone in the motion pic¬ 
ture business should have a 
copy.” 

M. Campbell, Chief Projectionist, 
Loew’s Theatres: “It has the 
premiere position in my techni¬ 
cal library—a necessary ad¬ 
junct to every projection 
room.” 

Morning Telegraph: “Written 
with the amateur in mind as 
well as the professional. 
Those using motion pictures in 
churches and school will be 
especially interested.” 

Ben Turner, Chief Projectionist, 
D. W. Griffith. “Your book 
unquestionably the best on the 
market. We use it.” 


Price Five Dollars 


THE TECHNICAL BOOK COMPANY 

























INDEX 


323 


C 

Cage Type of Aerial. 64 

Calculation of Eesistance. 25 

Capacitive Coupling . 92 

Care of Battery . 261 

Care of Eadiotron Tubes . 128 

Care of Eeceiving Sets . 175 

Cartridge Fuse . 166 

Cascade Amplification . 150 

Cause and Eemedy of Generator Troubles. 273 

Characteristics of Coil Antennas. 85 

Charging Batteries . 264 

Coil Aerials .62-78 

Combination of Electron Tube Amplifier and Crystal 

Detector . 159 

Combination Eadio & Audio Eegenerative Amplification.. 160 

Complete Aerial Outfit . 88 

Complete Eeceiving Set on Common Base. 225 

Condenser . 212 

Condenser, Fixed .... 212 

Condenser, Two-Plate . 216 

Condenser, Variable . 216 

Conductance . 22 

Connections for using Tube as a Detector. 141 

Construction of Aerial . 71 

Construction of Crystal Detector . 191 

Construction of Crystal Eeceiving Set. 175 

Construction of Double Slide Tuner. 222 

Construction of Fixed Condenser . 212 

Construction of Loose Coupler . 218 

Construction of Eeactance Coil . 58 

Construction of Eegenerative Eeceiving Sets. 177 

Construction of Elieostats . 46 

Construction of Tuning Coil . 224 

Construction of Transmitting Sets . 103 

Construction of Vacuum Tubes. 128 

Construction of Variable Condenser . 215 

Construction of Vario Coupler . 216 

Construction of Variometer . 217 

Contact Switch . 102 

Copper Losses in Transformer. 54 

Core Losses in Transformers. 54 

Correct Method of Setting Brushes. 274 

Counterpoise Antenna . 68 

Coupled Circuits . 90 














































324 TEXT BOOK ON RADIO 


Motors 

AND 

Motor-Generators 

Their Construction, Operation and Care 
By JAMES R. CAMERON 
140 Pages Fully Illustrated 

PRICE ONE DOLLAR 


Electricity 

For the 

Motion Picture Operator 
By JAMES R. CAMERON 
140 Pages Fully Illustrated 


PRICE ONE DOLLAR 

From All Book Stores and Dealers or Direct 

THE TECHNICAL BOOK COMPANY 

NEW YORK CITY 








INDEX 325 


Crystal Detector . 191 

Crystal Deceiving Sets . 175 

Current . 22 

Cycles . 40 

D 

Damping. 93 

Detector . 191 

Diagram of Elementary Rheostat . 46 

Diagram of Elementary Transformer . 53 

Diagram of Generator . 34 

Diagram of N. Y. “Times” Receiving Set. 174 

Diagram of Telemegaphone . 227 

Diagram of Vacuum Tube. 138 

Direct Coupling. 90 

Direct Current C. W. and I. C. W. Circuit. 123 

Direction of Current. 267 

Discharging Batteries . 268 

Double Slide Tuner. 222 

E 

Edison Effect . 130 

Electrical Resistance . 45 

Electricity . 21 

Electrolyte . 264 

Electro-Motive Force . 22 

Electron Tube Amplifier with Crystal Detector. 161 

Electron Tube as a Detector . 139 

Electron Tube as a Generator . 162 

Elementary Theory of Amplification. 152 

Elimination of Interference . 205 

Energy. 26 

Equivalent of Electrical Energy in Mechanical Units.... 28 
Excessive Speed (Motors). 284 

F 

Fading . U5 

Failure of Motor to start. 282 

Fan Type of Aerial . 64 

Feed-back Action . 163 

Fixed Condensers . 212 

Four Bearing Ring Oiled Set. 35 

Free Oscillations .;. 96 

Frequency . 39 

Fuses . 166 











































326 TEXT BOOK ON RADIO 


RADIO for BEGINNERS 

By James R. Cameron 


A complete guide to Radio work detailed in 
simple terms. Specific helpfulness as to the 
operation and care of each make and type of 
outfit. Adjustment and repair—how to detect 
and correct faults in your set—wiring dia¬ 
grams—profuse illustrations — tables — charts, 
and data on various problems that confront 
the beginner. 

Price One Dollar 


Ask your Dealer today 
or 

THE TECHNICAL 
BOOK COMPANY 







INDEX 327 


G 

General Storage Battery Data. 262 

Generation of Electricity. 31 

Generator . 34 

Generator—Three Unit . 33 

Generator Troubles, their cause and remedy. 273 

Glossary of Badio Terms. 297 

Grid Leak . 145 

Ground Clamps . 61 

Ground Connections . 63 

Ground Systems . 63 

H 

Hard Tubes . 132 

How to Build a Super-Begenerative Beceiving Set. 231 

How to Erect an Aerial. 71 

How to Install a Beceiving Set . 193 

How to Make a Fixed Condenser . 212 

How to Make a Beactance Coil . 58 

How to Make a Tuning Coil . 224 

How to Make a Variocoupler . 216 

How to Tune for Waves of Known Length . 203 

How to Tune for Waves of Unknown Length. 203 

How We Hear Music and Speech by Wireless.. 5 

I 

Idle Batteries . 271 

Incorrect Speed (Motor) . 284 

Indications of a Complete Battery Charge. 266 

Indoor Aerials . 84 

Inductance . 41 

Induction . 53 

Inductive Coupling . 91 

Installation of Aerial . 71 

Installation of Detector and Two Stage Amplifier. 207 

Installation of Grebe Beceiving Sets . 193 

Installation of Intermediate Wave Begenerative Sets. . . . 197 

Installation of Lightning Protective Device. 75 

Installation of Loud Speakers . 226 

Installation of Two Stage Amplifier. 208 

Installation of Westinghouse Beceiving Sets . 177 

Installation of Westinghouse Transmitting Sets . 103 

Instructions for Care of Batteries . 264 










































328 TEXT BOOK ON RADIO 


HOW TO 

BUILD YOUR OWN 
RECEIVING SET 


A BOOKLET WRITTEN FOR 
THOSE WHO KNOW LITTLE 
OR NOTHING OF THE SUB¬ 
JECT OF RADIO 


Price Twenty-five Cents 

From All Dealers 
or Direct 

THE TECHNICAL 
BOOK COMPANY 










* INDEX 329 


Instructions for Care of Badiotron Tubes. 150 

Interference—Elimination of . 206 

Internal Construction of a Two Plate Condenser. 216 


L 


Life of Badiotron Tube . 150 

Lightning Protective Device . 75 

Lightning Switch . 75 

Locating a Grounded Coil in Generator. 276 

Locating a Short Circuit Coil in Generator. 278 

Location of Faults in Beceiving Sets.194-198 

Loop Aerial . 86 

Loose Coupler . 218 

Losses in Transformers . 52 * 

Loud Speakers . 226 


M 


Method of Connecting Ground Clamps. 61 

Microphone Transmitter . 114 

Modulated C. W. Signals. 204 

Motor, Befuses to Start . 282 

Motor, Bunning in Wrong Direction. 286 

Motor, Troubles and Bemedies . 282 


0 


Ohms Law 
Operation of Aeriola, Sr 


29 

186 


Operation of Crystal Sets . 175 

Operation of Grebe Beceiving Sets . 193 

Operation of Westinghouse, E. C. Beceiving Sets. 181 

Operation of Westinghouse Tube Transmitting Sets .... 104 

Overheated Bearings . 278 

Overheating of Motor Starter. 285 

Overheating of the Armature . 275 


P 


Plate Condenser . 

Polarity . 

Polarity, Storage Battery . 

Power . 

Protective Devices . 

Putting Batteries Into Commission 


216 

264 

264 

27 

89 

271 






































330 TEXT BOOK ON RADIO 


RADIO 

DICTIONARY 


With Useful Tables and 
Information for the Radio Fan 


A Book That Fits 
the Vest Pocket 


Price 50 Cents 

From Your Dealer or Direct 
from the Publishers 


THE TECHNICAL 
BOOK COMPANY 










INDEX 331 


Q 

Quantity . 26 

R 

Radio Frequencies . 43 

Radio Terms . 297 

Radiophone Circuit . 121 

Radiotelephony . 120 

Radiotron Tubes . 128 

Reactance . 42 

Reactance Coil . 58 

Receivers Used as Wave Meters. 204 

Receiving Sets, Care of . 169 

Receiving Sets, Faults and Remedies . 194 

Receiving Sets, Operation of . 193 

Receiving Set on Common Base . 225 

Regenerative Amplification . 157 

Regenerative Circuit for Simultaneous Amplifying and 

Rectifying . 155 

Regenerative Receiver Sets . 210 

Regulations for the Installation of Aerials. 288 

Requirements of National Electrical Code—Radio Installa¬ 
tion . 291 

Resistance Affected by Heating . 25 

Resistance Coils . 46 

Resistance Coupled Amplifier . 151 

Resistance, Electrical .23-45 

Resistance Proportional to Length . 24 

Resistance Inversely Proportional to Cross Section. 24 

Resonance Transformer . 57 

Restoring Weakened Cells . 268 

Rheostats . 46 

Rheostats in Multiple. 50 

Rule for Wave Length. 167 

S 

Secondary Coil . 53 

Sediment in Cells .26-4 

Self Induction . 55 

Self Rectifying C. W. Telegraph Circuit. 127 

Soft Tubes. 132 

Spark Signals . 203 

Sparking of Motor . 282 









































332 TEXT BOOK ON RADIO 


Books by the Same Author 

MOTION PICTURE PROJECTION 

1060 Pages Third Edition 500 Illustrations 

Price Five Dollars 

ELEMENTARY TEXT BOOK ON PROJEC¬ 
TION 

The Text Book used by the American Red Cross, Y. M. C. 
A., Knights of Columbus, Etc., Etc. 

Price Two Dollars 

TEXT BOOK ON RADIO 

350 Pages Fully Illustrated 

Price 

Two-Fifty—Cloth Three Dollars—Flexo-Leatho. 

MOTORS AND MOTOR-GENERATORS 

140 Pages Flexible Covers 

Price—One Dollar 

ELECTRICITY FOR MOTION PICTURE 

OPERATORS 

140 Pages Flexible Covers 

Price One Dollar 

EXAMINATION QUESTIONS AND 
ANSWERS 

On Motion Picture Projection 
140 Pages Flexible Covers 

One Dollar 

POCKET REFERENCE BOOK FOR PRO¬ 
JECTIONISTS 

160 Pages Flexible Cover 

One Dollar 

RADIO FOR BEGINNERS 

160 Pages Fully Illustrated 

Price One Dollar 

RADIO DICTIONARY 

Fifty Cents 

HOW TO BUILD YOUR OWN RADIO SET 

Twentv-five Cents 






INDEX 333 


Special Tuning Instructions. 203 

Specific Resistance . 25 

Stabilizer . 157 

Storage Battery Charging Circuit . 270 

Storage Batteries . 261 

Sulphating . 272 

Switch, Lightning . 75 

T 

“T” Aerial . 65 

Telegraphing . 105 

Telemegaphone . 227 

Telephone Receiver . 116 

Telephony .. 105 

Test of Specific Gravity.... 266 

Theory of Amplification . 152 

Theory of Production and Reception of Electro-Magnetic 

Waves . 16 

Three Unit Generator Set. . 33 

To Build a Super-Regenerator Receiving Set. 253 

To Find Amperes . 30 

To Find Resistance . 30 

To Find Resistance of Copper Wires. 30 

To Find Voltage. 30 

To Find Watts . 30 

Transformers . 51 

Transmitting Sets . 103 

Tube as Amplifier . 146 

Tube—Construction of . 130 

Tube Transmitter . 103 

Tuning Method for Three Circuit Receivers. 201 

Tuning Method for Two Circuit Receivers. 202 

Tuning for Signals of Known Length . 203 

Tuning for Signals of Unknown Length . 203 

Two Electrode Tube . 131 

Two Plate Condenser . 216 

U 

Units of Double Slide Tuner.223 

U. S. Radio Laws and Regulations. 294 

V 

Vacuum Tubes . 123 

Variable Condenser . 215 










































334 


TEXT BOOK ON BADIO 


James R. Cameron’s Text Books 

Can Be Had From 

American News Co., New York City, N. Y. 

Chas. Scribners’ Sons, Fifth Ave., New York, N. Y. 
Baker & Taylor, New York City, N. Y. 

G. P. Putnam’s Son, 6 W. 45th St., New York, N. Y. 
Macey’s Dept. Store, Broadway, New York, N. Y. 
Howell’s Cine Equip. Corp., 729 Seventh Ave., 

_ N. Y., N. Y. 

Motion Picture Equip. Co., 717 Seventh Ave., N. Y., 
N. Y. 

United Theatre Equip. Corp., 729 Seventh Ave., 
N. Y., N. Y. 

Al. Becker, 184 Franklin St., Buffalo, N. Y. 

Otto Ulbrich & Co., 386 Main St., Buffalo, N. Y. 
Auburn Theatrical Supply Co., Auburn, N. Y. 

Marshall Fields, Chicago, Ill. 

A. C. McClurg, Chicago, Ill. 

United Theatre Equipment, Chicago, Ill. 

M. P. Equipment Corp., Vine St., Philadelphia, Pa. 

Old Corner Book Store, Inc., Bromfield St., Boston, Mass. 
Williams Book Store Co., Boston, Mass. 

De Wolfe & Fiske Co., Boston, Mass. 

Michigan M. P. Supply Co., Detroit, Mich. 

Argus Enterprises, Inc., Denver, Colorado. 

Scott Leslie, Tampa, Fla. 

Walter G. Preddy, Golden Gate Ave., San Francisco, Cal. 
Paul Elder & Co., 239 Post St., San Francisco, Cal. 

New Biggins Book Store Co., San Francisco, Cal. 

Sather Gate Book Store, 2307 Telegraph Ave., Berkeley, 
Cal. 

Teco Products Corp., Loeb Arcade, Minneapolis, Minn. 
Lucas Theatre Supply Co., Dallas, Texas. 

Lucas Theatre Supply Co., Atlanta, Ga. 





INDEX 335 


Variable Contact Switch . 102 

Yariocoupler . 216 

Variometer .213-217 

Vernier Rheostat . 47 

Victrola Attachment . 229 

Vocarola . 228 

W 

Watt, The . 28 

Wavelength. 167 

Westinghouse Aerial Outfit . 88 

Westinghouse Aeriola Grand . 184 

Westinghouse Crystal Receiving Set. 175 

Westinghouse Loud Speaker . 229 

Westinghouse R. C. Set . 177 

Westinghouse Tube Transmitter . 103 

What Happens in a Receiving Set . 10-> 

What Happens in a Transmitting Set . 101 

What is meant by Wavelength. 167 

Wire Telegraphy and Telephony. HI 

Wiring Diagram Regenerative Receiving Set Using Honey¬ 

comb Coils .. 200 
























336 TEXT BOOK ON EADIO 


James R. Cameron’s Text Books 

Can Be Had From 

Conner 6c Conner, Wabash, Inch 
The U. T. E. Corp., Omaha, Neb. 

College Book Store, Ames, Iowa 
A. J. Wolfson, 101 Washington St., Seattle, Wash. 
Dwyer Bros. 6c Co., 520 B’way, Cincinnati, Ohio 
U. T. E. Corp., Oklahoma City, Okla. 

Queen Service Co., Birmingham, Ala. 

J. K. Gill 6c Co., Portland, Oregon 

CANADA 

Perkins, Ladd Electric Co., Montreal 
Perkins, Ladd Electric Co., Toronto 
Regina Book Store, Scarth St., Regina, Sask. 

Canada Book Co., Ltd., Regina, Sask. 

ENGLAND 

Sidney Rented, 36 Maiden Lane, London 
D. P. Howell’s, Charing Cross Road, London 
G. E. Stechert 6c Co., Carey St., London 

PARIS 

G. E. Stechert 6c Co., 16 Rue De Conde 

SOUTH AFRICA 

Hardt 6c Bell, Capetown 

AUSTRALIA 

Thos. Heide, Kiewa St., Albany, New South Wales 
Whitcombe 6c Tombs, Melbourne 6c London 

NEW ZEALAND 
Whitcombe 6c Tombs, Ltd., Auckland 
Whitcombe 6c Tombs, Ltd., Wellington 





TEXT BOOK ON RADIO 


You Take No Chances When You 
Buy Cameron’s Text Books 

They Are Used and Endorsed By 

United States War Dept., Washington, D. C. 

United States Army Dept., Washington. D. C. 

United States Navy Dept., Washington, D. C. 

United States Dept, of Agriculture, Washington, D. C. 

United States Treasury Dept., Washington, D. C. 

United States Public Health Dept., Washington, D. C. 

United States Dept, of Public Instruction, Washington, D. C. 

Dept, of Education, New York 
Dept, of Education, Newark, N. J. 

Dept, of Education, Chicago, Ill. 

Dept, of Education, Detroit, Mich. 

Dept, of Education, Boston, Mass. 

Dept, of Education, Philadelphia, Pa. 

Dept, of Education, Montreal, Canada 
Dept, of Education, St. Paul, Minn. 

State Education Assn., Pennsylvania 
State College, Iowa 
University of Kansas 

Dept, of Commercial Economics, Washington, D. C. 

Alabama Polytechnic Institute 

Rankin School of Mechanical Trades, St. Louis, Mo. 

Dakota Agriculture College, N. Dakota 
Darlington Seminary, Westchester, Pa. 

American Library Association 

Dept, of Visual Instruction, Detroit, Mich. 

National Committee on Conservation, Chicago 
U. S. Soldiers Home Washington, D. C. 

Libraries Throughout the World 

Mound Consolidated Schools, Mound, Minn. 

New York State Educational Society 
Methodist Episcopalian Convention Committee 
American Institute of Cinematography, Chicago, Ill. 

Community M. P. Bureau 


Knights of Columbus 
Y. M. C. A. 

Motion Picture News 
New York Times 
Exhibitors Trade Review 
Exhibitors Herald 
Morning Telegraph 
Simplex Machine Co. 

Acme Machine Co. 
Westinghouse Elec. Co. 
Hertner Electric Co. 
National Cash Register Co. 


American Red Cross 
Statler Hotels 
Baltimore Sun 
Boston Transcript 
Screen Magazine 
Moving Picture Age 
Reel Journal 
Powers Machine Co. 
Eastman Kodak Co. 
General Electric Co. 
Gundlach Optical Co. 
Ansco Co. 


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22 





MEMORANDUM 




MEMORANDUM 





MEMORANDUM 





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MEMORANDUM 






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